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Abstract

This review will first describe the importance of Ca²⁺ entry for function of excitable cells, and the subsequent discovery of voltage-activated calcium conductances in these cells. This finding was rapidly followed by the identification of multiple subtypes of calcium conductance in different tissues. These were initially termed low- and high-voltage activated currents, but were then further subdivided into L-, N-, PQ-, R- and T-type calcium currents on the basis of differing pharmacology, voltage-dependent and kinetic properties, and single channel conductance. Purification of skeletal muscle calcium channels allowed the molecular identification of the pore-forming and auxiliary α₂δ, β and ϒ subunits present in these calcium channel complexes. These advances then led to the cloning of the different subunits, which permitted molecular characterisation, to match the cloned channels with physiological function. Studies with knockout and other mutant mice then allowed further investigation of physiological and pathophysiological roles of calcium channels. In terms of pharmacology, cardiovascular L-type channels are targets for the widely used antihypertensive 1,4-dihydropyridines and other calcium channel blockers, N-type channels are a drug target in pain, and α₂δ-1 is the therapeutic target of the gabapentinoid drugs, used in neuropathic pain. Recent structural advances have allowed a deeper understanding of Ca²⁺ permeation through the channel pore and the structure of both the pore-forming and auxiliary subunits. Voltage-gated calcium channels are subject to multiple pathways of modulation by G-protein and second messenger regulation. Furthermore, their trafficking pathways, subcellular localisation and functional specificity are the subjects of active investigation.

Keywords

Calcium channel voltage second messenger neuron heart

Introduction: the importance of Ca²⁺ entry for function of excitable cells

It has been clear from the time of Sydney Ringer, working at University College London, that calcium ions (Ca²⁺) are essential for heart muscle contraction (Ringer, 1883). However, the paramount importance of Na⁺ and K⁺ for the activation and inactivation underlying action potential generation led to Ca²⁺ permeation being little studied for many years. In the 1950’s Paul Fatt, working at University College London with both Katz and Ginsborg, found that Ca²⁺ supports action potential-like spikes in crustacean muscle (Fatt and Ginsborg, 1958; Fatt and Katz, 1953), and this was also found to be true in barnacle muscle (Hagiwara and Takahashi, 1967). When it was also identified that Ca²⁺ was essential for neurotransmitter release (Katz and Miledi, 1967), it became clear that calcium ion entry through membranes was key to many important processes in nerves as well as muscle. These key players in the field are pictured in Figure 1(a)–(d).

Figure 1.

Some key figures in the early discovery of calcium channels and their pharmacology: (a) Bernard Katz, (b) Susumu Hagiwara, (c) Paul Fatt, (d) Bernard Ginsborg (right) demonstrating equipment similar to that used to record crustacean muscle action potentials, (e) Harald Reuter and (f) Albrecht Fleckenstein. (c) is taken from a photograph (1978) by Martin Rosenberg, the Physiological Society; reproduced with permission; (a), (b) and (f) are reproduced from with permission from Richard W. Tsien (Barrett and Tsien, 2004); (d) is reproduced with permission from Bernard Ginsborg, who died this year (1925–2018).

Identification of multiple subtypes of calcium channel

A major contribution to the understanding of calcium channel function then came from Harald Reuter (Figure 1(e)), who showed, using microelectrodes, that calcium currents were present in voltage-clamped cardiac Purkinje fibres (Reuter, 1967). The advent of the gigaseal patch-clamp method for recording currents through the membrane of single cells (Hamill et al., 1981) then allowed single calcium channels to be resolved (Fenwick et al., 1982).

The discovery and use of verapamil, and the 1,4-dihydropyridines (DHPs) including nifedipine, as antihypertensive drugs represented a very important advance (Fleckenstein, 1983) (Figure 1(f)). Their target was found to be inhibition of cardiovascular calcium channels (Lee and Tsien, 1983); thus, the term calcium channel blocker or antagonist was coined. Related drugs were found to have agonist effects (Schramm et al., 1983), to increase cardiac calcium conductance and prolong single channel openings (Hess et al., 1984). Both the agonist and antagonist drugs gave researchers important tools to dissect calcium channel function in a variety of tissues.

The first suggestion that there was more than one component to calcium currents in different tissues came from the group of Hagiwara et al. (1975), followed by evidence of low threshold Ca²⁺ spikes in mammalian central neurons (Llinás and Yarom, 1981), and distinct low voltage-activated currents in peripheral dorsal root ganglion neurons (Carbone and Lux, 1984; Fedulova et al., 1985; Nilius et al., 1985).

Identification of N-, P- and R-type calcium currents as distinct from L-type channels

In dorsal root ganglion (DRG) neurons, it was then found that there were three calcium current components. The DHP-sensitive current was designated L-type (for long-lasting, which also had a large singe channel conductance) and the low-voltage activated component was termed T (for transient, which also had a Tiny single channel conductance). A third component, which was high-voltage activated but DHP-insensitive, was termed N-type (neither L nor T, and also exclusively Neuronal) (Fox et al., 1987; Nowycky et al., 1985) (Figure 2(a)). A blocker of this component was not long in appearing. A toxin component from the marine snail Conus geographus, ω-conotoxin GVIA, first thought to block both neuronal L- and N-type calcium currents (McCleskey et al., 1987), was later found to be highly selective for N-type channels (Boland et al., 1994; Plummer et al., 1989). Using this pharmacological blocker, N-type calcium currents were then shown to play a key role in neurotransmitter release (Hirning et al., 1988).

Figure 2.

Single calcium channels with different properties, and topology of the channels. (a) Identification of a third component of voltage-gated calcium channels (N-type) from the biophysical properties of single channel currents observed in cell-attached patches on dorsal root ganglion neurons. Redrawn from Nowycky et al. (1985). TP: test potential; HP: holding potential. Reproduced with thanks to Richard W. Tsien. (b) Diagram of α₁ subunit topology and calcium channel subunit structure, also showing α₂δ (purple) and β (blue). ϒ₁ is only present in skeletal muscle calcium channel complexes. S4 voltage sensors in each α₁ domain are represented by red transmembrane segments. Yellow denotes S5 and S6 pore transmembrane segments in each domain.

The importance of pharmacological tools in the discovery of calcium channel subtypes became even more evident when it was found that the calcium current in Purkinje neurons was not blocked by DHPs or by ω-conotoxin GVIA. This current was called P-type (for Purkinje) (Llinás et al., 1989). The same group used a polyamine toxin (FTX) from the American funnel web spider to block Purkinje cell Ca²⁺ currents, but FTX was not particularly selective for P-type channels, whereas a peptide toxin component from the same spider (ω-agatoxin IVA) was more selective, blocking fully the calcium current in Purkinje neurons (Mintz et al., 1992). This toxin also inhibited a component of the calcium current in cerebellar granule cells (Pearson et al., 1995; Randall and Tsien, 1995), which was initially termed Q-type as it had different biophysical properties from that in Purkinje neurons (Randall and Tsien, 1995); however, these are usually now called PQ currents. That study also identified an additional resistant current component in cerebellar granule cells which was designated R-type (Randall and Tsien, 1995), and a similar novel component was also identified in bullfrog sympathetic neurons (Elmslie et al., 1994). A tarantula toxin, SNX-482, was identified to block this component (Newcomb et al., 1998), but it has subsequently been found also to block other channels (Kimm and Bean, 2014), complicating interpretation of physiological experiments using SNX-482.

Purification and molecular identification of the calcium channel subtypes

Receptors for the DHP calcium antagonists were identified using [³H]-nitrendipine to guide purification. They were found to be highly concentrated in the t-tubules of skeletal muscle (Fosset et al., 1983), where they were shown to be responsible for charge movement and excitation-contraction coupling (Rios and Brum, 1987). Purification studies identified the skeletal muscle DHP receptor to be a complex of five polypeptides in approximately equal amounts, and therefore considered to be subunits. They were termed, in decreasing order of size, the α₁, α₂, β, ϒ and δ subunits (Hosey et al., 1987; Takahashi et al., 1987). The 175 kDa α₁ subunit was tentatively identified as the pore-forming subunit of the channel, since it bound radiolabelled DHP. The associated proteins were termed auxiliary or accessory subunits.

Peptide sequence from the purified DHP receptor protein enabled the identification of probes and subsequent cloning of the skeletal muscle calcium channel (Ellis et al., 1988; Tanabe et al., 1987). The hydropathy plot indicated that it was a 24 transmembrane spanning protein, with four homologous repeated domains joined by intracellular linkers, similar to recently cloned voltage-gated Na⁺ channel (Noda et al., 1984) (Figure 2(b)). This protein was termed α₁S (for skeletal muscle) and was indisputably shown to encode a calcium channel by injection of its cDNA into dysgenic skeletal myotubes which lack the mRNA for α₁S (Tanabe et al., 1988). This restored excitation–contraction coupling, as well as the very slow calcium current observed in native skeletal muscle.

The cardiac L-type calcium channel, termed α₁C, was then cloned by homology with α₁S (Mikami et al., 1989). Prior to this time, the unique permeation selectivity of the voltage-gated calcium channels for Ca²⁺ had already been attributed to high affinity Ca²⁺ binding in the pore of the channel (Hess and Tsien, 1984), and this was borne out by identification of key glutamate residues in the pore ‘P loops’ (Yang et al., 1993), whose acidic side chains were surmised to participate in Ca (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid)²⁺ binding and permeation.

Several brain calcium channels were then cloned and identified to encode P- and N-type channels (Mori et al., 1991; Snutch et al., 1990; Starr et al., 1991). These were termed α₁A and α₁B, respectively. Another channel was cloned and dubbed α₁E (Soong et al., 1993). It was first classified as a low-voltage activated T-type channel, but it soon became clear that it did not have the expected properties, and it is now considered to encode R-type channels. Genes for three T-type channels were later cloned by Perez-Reyes and colleagues (Cribbs et al., 1998; Lee et al., 1999; Perez-Reyes et al., 1998). These were termed α₁G, H and I. In addition, two further L-type channels were identified. The first, cloned from brain, was called α₁D (Williams et al., 1992) and was shown to have distinctive biophysical properties, being lower voltage-activated than α₁C (Koschak et al., 2001; Xu and Lipscombe, 2001). Finally, a fourth L-type channel was identified because of its role in a genetic form of night blindness (Bech et al., 1998; Strom et al., 1998), and this was also shown to have properties distinguishing it from the other L-type channels (Koschak et al., 2003).

Following the cloning and initial study of all the calcium channel α₁ subunits identified in the mammalian genome, a rationalised nomenclature was adopted in 2000, grouping the α₁ subunits into Ca_V1 (L-type), Ca_V2 (non-L-type) and Ca_V3 (T-type) (Ertel et al., 2000) (Table 1). Since that time the distinctive properties of multiple splice variants of these channels have also been recognised.

Table 1.

Subtypes of calcium channel.

Activation voltage	Functional nomenclature	Channel α₁ subunit	Ca_V nomenclature	Main function
(High)	L	a₁S	1.1	Skeletal muscle voltage sensor
High	L	a₁C	1.2	Cardiac, smooth muscle function
Medium	L	a₁D	1.3	Hearing, sino-atrial node function
Medium	L	a₁F	1.4	Retinal neurotransmission
High	PQ	a₁A	2.1	Synaptic transmission in CNS, motor nerves and elsewhere
High	N	a₁B	2.2	Synaptic transmission in PNS (and CNS, especially early in development)
Medium	R	a₁E	2.3	Present in some neurons and synapses
Low	T	a₁G	3.1	Neuronal excitability, pacemaker activity, subthreshold oscillations
Low	T	a₁H	3.2
Low	T	a₁I	3.3

PNS: peripheral nervous system; CNS: central nervous system.

Importance of auxiliary subunits

The auxiliary β subunit from skeletal muscle was the first to be cloned (Ruth et al., 1989) (Figure 2(b)). It was subsequently termed β_1a, after three further isoforms (β₂, β₃ and β₄) as well as multiple splice variants were identified by homology. β_1b is the non-muscle splice variant of β₁ (Pragnell et al., 1991), and β_2a is a palmitoylated β₂ splice variant, giving it distinctive properties (Qin et al., 1998). The importance of these β subunits to the expression of the Ca_V1 and Ca_V2 channels was clear from antisense knockdown studies in native tissues and early expression studies (Berrow et al., 1995; Qin et al., 1998). In contrast, the Ca_V3 channels do not appear to have any obligate auxiliary subunits.

When the auxiliary α₂δ subunit was cloned, it was realised that α₂ and δ are encoded by the same gene and form a pre-protein, which is then proteolytically cleaved, but the α₂ and δ proteins remain associated by pre-formed disulphide bonding (De Jongh et al., 1990; Jay et al., 1991). Its proteolytic cleavage has recently been shown to be essential for α₂δ function (Kadurin et al., 2016). The skeletal muscle α₂δ was subsequently termed α₂δ-1, when three further mammalian isoforms were identified: α₂δ-2 (Barclay et al., 2001; Gao et al., 2000), α₂δ-3 and α₂δ-4 (Qin et al., 2002). The muscle α₂δ subunit was first described as a transmembrane protein, but they have subsequently been shown to be glycosyl-phosphatidylinositol (GPI)-anchored into the outer leaflet of the plasma membrane (Davies et al., 2010) (Figure 2(b)). The α₂δ subunit was predicted to contain a von Willebrand factor A (VWA) domain, which was found to be essential for trafficking, both of α₂δ itself, and for its effect on the α₁ subunits (Canti et al., 2005; Cassidy et al., 2014; Hoppa et al., 2012).

The skeletal muscle calcium channel complex also contains a ϒ subunit, now called ϒ₁ (Takahashi et al., 1987) (Figure 2(b)), but ϒ is not associated with other calcium channels, and further members of this ‘ϒ subunit’ family are now known to be trafficking proteins that modulate the function of AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) glutamate receptors, rather than voltage-gated calcium channel subunits (Tomita et al., 2003). The roles of the different calcium channel auxiliary subunits have been more extensively reviewed recently (Dolphin, 2012).

Elucidation of physiological channel function from knockout mouse studies and genetic mutations

Several spontaneously arising mouse loss-of-function mutants were identified which gave important clues as to the function of the channel subunits. This was particularly true for Ca_V2.1, β4 and α₂δ-2 which are strongly expressed in cerebellum, and whose mutation produced obvious ataxias (Barclay et al., 2001; Burgess et al., 1997; Fletcher et al., 1996). Subsequent targeted knockouts gave similar phenotypes. A surprise came with the knockout of Ca_V1.3, both in mice and in a homozygous human mutation, in whom the main phenotype was deafness and sino-atrial node dysfunction (Baig et al., 2011). Furthermore Ca_V1.4 was identified from its role in a retinal disease (Bech-Hansen et al., 1998; Strom et al., 1998), and the knockout mouse has a similar phenotype (Mansergh et al., 2005). Knockout of Ca_V2.2 resulted in a diminution of neuropathic pain responses, reinforcing its importance in primary afferent neurotransmission (Saegusa et al., 2001). Similarly, α₂δ-1 knockout delayed the onset of mechanical hyperalgesia following neuropathic injury (Patel et al., 2013) and α₂δ-3 has a role in hearing (Pirone et al., 2014), and in the central control of pain (Neely et al., 2010).

Structural studies

The first components of the calcium channel complex to be amenable to structural studies were the β subunits, which contain two conserved interacting domains (SH3 and guanylate kinase-like), the latter binding to the linker between domains I and II of the channels (Chen et al., 2004; Opatowsky et al., 2004; Pragnell et al., 1994; Richards et al., 2004; Van Petegem et al., 2004).

The first crystal structure for a calcium-selective voltage-gated channel was obtained using a mutant form of a bacterial sodium channel homolog, Na_VAb, a single domain channel which forms homo-tetramers (Payandeh et al., 2011). This was mutated so that the pore became Ca²⁺-selective, forming Ca_VAb. This structure has provided multiple insights, including confirmation of the Ca²⁺ permeation process (Tang et al., 2014). Remarkably, this channel was sensitive to calcium channel antagonists, yielding further important insight into the binding and mechanism of action of these drugs (Tang et al., 2016). For mammalian calcium channel complexes, although low-resolution single particle electron microscopic structures were published previously (Serysheva et al., 2002; Walsh et al., 2009; Wolf et al., 2003), major advances in cryo-electron microscopy were needed before a detailed structure of the skeletal muscle calcium channel was produced, very beautifully elucidating details of the pore and the subunit arrangement (Wu et al., 2016). GPI-anchoring of α₂δ (Davies et al., 2010), and interaction of the α1 subunit with the VWA and Cache domains (which have similarity to bacterial chemotaxis domains) of α₂δ (Canti et al., 2005; Cassidy et al., 2014), were confirmed in the structure (Wu et al., 2016).

Calcium channel modulation

Only two canonical second messenger modulation pathways will be considered here, for reasons of space: inhibitory modulation of neuronal calcium channels by G-proteins, and cyclic AMP-dependent phosphorylation, mediating enhancement of L-type channels. Many other pathways also deserve mention, including Ca²⁺-calmodulin control of Ca²⁺-dependent inactivation and facilitation of L-type and P-type channels, studied extensively by the late David Yue (Dick et al., 2008; Peterson et al., 1999).

G-protein modulation

Voltage-dependent activation of neuronal calcium channels is required for neurotransmitter release, and this process can be inhibited by a range of modulatory neurotransmitters coupled to seven-transmembrane receptors (Dolphin, 1982; Jessell and Iversen, 1977; Peng and Frank, 1989), leading to the view that inhibitory modulation of the calcium channel-mediated component of the presynaptic action potential underpins receptor-mediated presynaptic inhibition (Dolphin et al., 1986; Dunlap and Fischbach, 1978; Ikeda and Schofield, 1989) (Figure 3(a)). Modulation of neurotransmitter release was found to be mediated by a pertussis toxin-sensitive GTP-binding protein, of the G_i/G_o family (Dolphin and Prestwich, 1985). The inhibitory modulation of neuronal calcium currents was subsequently also identified to involve these G-proteins (Scott and Dolphin, 1986; Holz et al., 1986) (Figure 3(c)). Using both native and cloned Ca_V2 channels, the modulation was subsequently shown to be a direct membrane-delimited effect of Gβϒ subunits (Herlitze et al., 1996; Ikeda, 1996), mediated by the channel I-II linker (Bourinet et al., 1996) and its intracellular N-terminus (Page et al., 1998). The characteristic voltage-dependence of the inhibition, which means that inhibition is lost with large or repeated depolarisations, was shown to require participation of the calcium channel β subunit (Meir et al., 2000).

Figure 3.

Inhibitory G-protein modulation of neuronal calcium channels. (a) Action potential (prolonged by K⁺ channel blockade), recorded from dorsal root ganglion neuron, showing the control, inhibition by the GABA-B agonist baclofen (100 μM) and recovery (from Figure 7 of Dolphin et al. (1986)). (b) Calcium channel currents recorded from dorsal root ganglion neuron, showing inhibition by baclofen (bac, 50 μM) (Dolphin et al., 1989). (c) Calcium channel currents recorded from Xenopus laevis oocytes injected with Ca_V2.2/β3/α₂δ-1 and the dopamine D2 receptor, showing inhibition by the D2 agonist quinpirole (100 nM) (replotted from Figure 2(e) of Canti et al. (2000).

Cyclic AMP-dependent phosphorylation

Another key example of second messenger modulation is provided by L-type calcium channels, which are potentiated by β-adrenergic receptor activation, via a cyclic AMP-dependent mechanism (Cachelin et al., 1983; Reuter, 1983). In heart, this effect is mediated by β1-adrenergic receptors and forms one of the main components of the fight-or-flight response. However, it has been difficult to reproduce when cloned Ca_V1.2 calcium channels are expressed, for example, in HEK-293 cells, suggesting it is more complex than simple channel phosphorylation, and indeed, the role of the several protein kinase A substrate serines in cardiac Ca_V1.2 function is still being determined (Lemke et al., 2008; Yang et al., 2016). Furthermore, the response to β-adrenergic stimulation may involve a proteolytically cleaved C-terminal fragment of the endogenous Ca_V1.2 channels (Fu et al., 2013; Fuller et al., 2010). Perhaps surprisingly, there appears to be a somewhat different basis for the spatially restricted stimulation observed in hippocampal neurons following activation by β2-adrenergic receptors of neuronal Ca_V1.2 channels (Qian et al., 2017).

Future research

The selective pharmacology that has been so important for dissecting out the functions of different calcium channels is still incomplete. Although a selective inhibitor of the T-type calcium channels exists (Dreyfus et al., 2010), it does not differentiate between the Ca_V3 channels. Similarly, there are currently no selective inhibitors of the different Ca_V1 channels. Such inhibitors that would be able to differentiate between these very similar channels could have important therapeutic possibilities. For example, selective inhibition of Ca_V3.2 could be of therapeutic benefit in certain types of pain (Marger et al., 2011), and selective inhibitors of Ca_V1.3 have potential for therapeutic use in Parkinson’s disease and other disorders (Striessnig et al., 2015). Furthermore, although ω-conotoxin GVIA is a selective blocker of N-type channels and a related compound is licenced for use intrathecally in some chronic pain conditions (Miljanich, 2004), no small molecule inhibitors of N-type channels have yet been shown to be effective in clinical trials for chronic pain.

Future challenges include a full understanding of how particular calcium channels are trafficked into precise subcellular domains, for example, how some channels are targeted to dendrites (Hall et al., 2013), while others are directed to presynaptic active zones to mediate neurotransmitter release (Kaeser et al., 2011). Furthermore, calcium channels have been found to interact, directly or indirectly, with multiple scaffolding proteins, ion channels and second messenger pathways (Müller et al., 2010), but how these are organised and function together remains to be elucidated. Related to this, the pathways for intracellular Ca²⁺ signalling to the nucleus and the selectivity for L-type Ca²⁺ channels in neurons are still being revealed (Cohen et al., 2015; Wheeler et al., 2012).

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research,authorship and/or publication of this article.

Funding

This work was supported by a Wellcome Trust Investigator award (098360/Z/12/Z) and a Royal Society Leverhulme Senior Fellowship to A.C.D.

References

Baig

Koschak

Lieb

et al . (2011) Loss of Ca(v)1.3 (CACNA1D) function in a human channelopathy with bradycardia and congenital deafness. Nature Neuroscience 14: 77–84.

Barclay

Balaguero

Mione

et al . (2001) Ducky mouse phenotype of epilepsy and ataxia is associated with mutations in the Cacna2d222 gene and decreased calcium channel current in cerebellar Purkinje cells. Journal of Neuroscience 21: 6095–6104.

Barrett

Tsien

(2004) Brief history of calcium channel discovery. In: Zamponi

(ed.) Voltage-Gated Calcium Channels. Dordrecht: Kluwer Academic/Plenum Publishers, pp. 1–21.

Bech-Hansen

Naylor

Maybaum

et al . (1998) Loss-of-function mutations in a calcium-channel α1-subunit gene in Xp11.23 cause incomplete X-linked congenital stationary night blindness. Nature Genetics 19: 264–267.

Berrow

Campbell

Fitzgerald

et al . (1995) Antisense depletion of beta-subunits modulates the biophysical and pharmacological properties of neuronal calcium channels. Journal of Physiology 482: 481–491.

Boland

Morrill

Bean

(1994) Omega-conotoxin block of N-type calcium channels in frog and rat sympathetic neurons. Journal of Neuroscience 14: 5011–5027.

Bourinet

Soong

Stea

et al . (1996) Determinants of the G protein-dependent opioid modulation of neuronal calcium channels. Proceedings of the National Academy of Sciences of the United States of America 93: 1486–1491.

Burgess

Jones

Meisler

et al . (1997) Mutation of the Ca²⁺ channel beta subunit gene Cchb4 is associated with ataxia and seizures in the lethargic (lh) mouse. Cell 88: 385–392.

Cachelin

De Peyer

Kokubun

et al . (1983) Ca²⁺ channel modulation by 8-bromocyclic AMP in cultured heart cells. Nature 304: 462–464.

10.

Canti

Bogdanov

Dolphin

(2000) Interaction between G proteins and accessory subunits in the regulation of α1B calcium channels in Xenopus oocytes. Journal of Physiology 527: 419–432.

11.

Canti

Nieto-Rostro

Foucault

et al . (2005) The metal-ion-dependent adhesion site in the Von Willebrand factor-A domain of alpha2delta subunits is key to trafficking voltage-gated Ca²⁺ channels. Proceedings of the National Academy of Sciences of the United States of America 102: 11230–11235.

12.

Carbone

Lux

(1984) A low voltage-activated fully inactivating Ca channel in vertebrate sensory neurones. Nature 310: 501–502.

13.

Cassidy

Ferron

Kadurin

et al . (2014) Functional exofacially tagged N-type calcium channels elucidate the interaction with auxiliary α₂δ-1 subunits. Proceedings of the National Academy of Sciences of the United States of America 111: 8979–8984.

14.

Chen

Zhang

et al . (2004) Structural basis of the alpha1-beta subunit interaction of voltage-gated Ca²⁺ channels. Nature 429: 675–680.

15.

Cohen

Tsien

et al . (2015) Evolutionary and functional perspectives on signaling from neuronal surface to nucleus.Biochemical and Biophysical Research Communications 460: 88–99.

16.

Cribbs

Lee

J-H

Yang

et al . (1998) Cloning and characterization of α1H from human heart, a member of the T type Ca²⁺ channel gene family. Circulation Research 83: 103–109.

17.

Davies

Kadurin

Alvarez-Laviada

et al . (2010) The α2δ subunits of voltage-gated calcium channels form GPI-anchored proteins, a post-translational modification essential for function. Proceedings of the National Academy of Sciences of the United States of America 107: 1654–1659.

18.

De Jongh

Warner

Catterall

(1990) Subunits of purified calcium channels: α2 and δ are encoded by the same gene. Journal of Biological Chemistry 265: 14738–14741.

19.

Dick

Tadross

Liang

et al . (2008) A modular switch for spatial Ca²⁺ selectivity in the calmodulin regulation of CaV channels. Nature 451: 830–834.

20.

Dolphin

(1982) Noradrenergic modulation of glutamate release in the cerebellum. Brain Research 252: 111–116.

21.

Dolphin

(2012) Calcium channel auxiliary alpha(2)delta and beta subunits: Trafficking and one step beyond. Nature Reviews Neuroscience 13: 542–555.

22.

Dolphin

Prestwich

(1985) Pertussis toxin reverses adenosine inhibition of neuronal glutamate release. Nature 316: 148–150.

23.

Dolphin

Forda

Scott

(1986) Calcium-dependent currents in cultured rat dorsal root ganglion neurones are inhibited by an adenosine analogue. Journal of Physiology 373: 47–61.

24.

Dolphin

McGuirk

Scott

(1989) An investigation into the mechanisms of inhibition of calcium channel currents in cultured sensory neurones of the rat by guanine nucleotide analogues and (–)– baclofen. British Journal of Pharmacology 97: 263–273.

25.

Dreyfus

Tscherter

Errington

et al . (2010) Selective T-type calcium channel block in thalamic neurons reveals channel redundancy and physiological impact of I(T)window. The Journal of Neuroscience 30: 99–109.

26.

Dunlap

Fischbach

(1978) Neurotransmitters decrease the calcium component of sensory neurone action potentials. Nature 276: 837–839.

27.

Ellis

Williams

Ways

et al . (1988) Sequence and expression of mRNAs encoding the α₁ and α₂ subunits of a DHP-sensitive calcium channel. Science 241: 1661–1664.

28.

Elmslie

Kammermeier

Jones

(1994) Reevaluation of Ca²⁺ channel types and their modulation in bullfrog sympathetic neurons. Neuron 13: 217–228.

29.

Ertel

Campbell

Harpold

et al . (2000) Nomenclature of voltage-gated calcium channels. Neuron 25: 533–535.

30.

Fatt

Ginsborg

(1958) The ionic requirements for the production of action potentials in crustacean muscle fibres. Journal of Physiology 142: 516–543.

31.

Fatt

Katz

(1953) The electrical properties of crustacean muscle fibres. Journal of Physiology 120: 171–204.

32.

Fedulova

Kostyuk

Veselovsky

(1985) Two types of calcium channels in the somatic membrane of new-born rat dorsal root ganglion neurones. Journal of Physiology 359: 431–446.

33.

Fenwick

Marty

Neher

(1982) Sodium and calcium channels in bovine chromaffin cells. Journal of Physiology 331: 599–635.

34.

Fleckenstein

(1983) History of calcium antagonists. Circulation Research 52: I3–16.

35.

Fletcher

Lutz

O’Sullivan

et al . (1996) Absence epilepsy in tottering mutant mice is associated with calcium channel defects. Cell 87: 607–617.

36.

Fosset

Jaimovich

Delpont

et al . (1983) [3H]nitrendipine receptors in skeletal muscle. Journal of Biological Chemistry 258: 6086–6092.

37.

Fox

Nowycky

Tsien

(1987) Single-channel recordings of three types of calcium channels in chick sensory neurones. Journal of Physiology 394: 173–200.

38.

Westenbroek

Scheuer

et al . (2013) Phosphorylation sites required for regulation of cardiac calcium channels in the fight-or-flight response. Proceedings of the National Academy of Sciences of the United States of America 110: 19621–19626.

39.

Fuller

Emrick

Sadilek

et al . (2010) Molecular mechanism of calcium channel regulation in the fight-or-flight response. Science signaling 3: ra70.

40.

Gao

Sekido

Maximov

et al . (2000) Functional properties of a new voltage-dependent calcium channel α₂δ auxiliary subunit gene (CACNA2D2). Journal of Biological Chemistry 275: 12237–12242.

41.

Hagiwara

Takahashi

(1967) Surface density of calcium ions and calcium spikes in the barnacle muscle fiber membrane. Journal of General Physiology 50: 583–601.

42.

Hagiwara

Ozawa

Sand

(1975) Voltage clamp analysis of two inward current mechanisms in the egg cell membrane of a starfish. Journal of General Physiology 65: 617–644.

43.

Hall

Dai

Tseng

et al . (2013) Competition between alpha-actinin and Ca(2)(+)-calmodulin controls surface retention of the L-type Ca(2)(+) channel Ca(V)1.2. Neuron 78: 483–497.

44.

Hamill

Marty

Neher

et al . (1981) Improved patch-clamp techniques for high resolution current recording from cells and cell-free membrane patches. Pflügers Archiv: European Journal of Physiology 391: 85–100.

45.

Herlitze

Garcia

Mackie

et al . (1996) Modulation of Ca²⁺ channels by G-protein β gamma subunits. Nature 380: 258–262.

46.

Hess

Tsien

(1984) Mechanism of ion permeation through calcium channels. Nature 309: 453–456.

47.

Hess

Lansman

Tsien

(1984) Different modes of Ca channel gating behaviour favoured by dihydropyridine Ca agonists and antagonists. Nature 311: 538–544.

48.

Hirning

Fox

McCleskey

et al . (1988) Dominant role of N-type Ca²⁺ channels in evoked release of norepinephrine from sympathetic neurons. Science 239: 57–60.

49.

Holz

GGI

Rane

Dunlap

(1986) GTP-binding proteins mediate transmitter inhibition of voltage-dependent calcium channels. Nature 319: 670–672.

50.

Hoppa

Lana

Margas

et al . (2012) Alpha2delta expression sets presynaptic calcium channel abundance and release probability. Nature 486: 122–125.

51.

Hosey

Barhanin

Schmid

et al . (1987) Photoaffinity labelling and phosphorylation of a 165 kilodalton peptide associated with dihydropyridine and phenylalkylamine-sensitive calcium channels. Biochemical and Biophysical Research Communications 147: 1137–1145.

52.

Ikeda

(1996) Voltage-dependent modulation of N-type calcium channels by G-protein beta gamma subunits. Nature 380: 255–258.

53.

Ikeda

Schofield

(1989) Somatostatin blocks a calcium current in rat sympathetic ganglion neurones. Journal of Physiology 409: 221–240.

54.

Jay

Sharp

Kahl

et al . (1991) Structural characterization of the dihydropyridine-sensitive calcium channel α₂-subunit and the associated delta peptides. Journal of Biological Chemistry 266: 3287–3293.

55.

Jessell

Iversen

(1977) Opiate analgesics inhibit substance P release from rat trigeminal nucleus. Nature 268: 549–551.

56.

Kadurin

Ferron

Rothwell

et al . (2016) Proteolytic maturation of α2δ represents a checkpoint for activation and neuronal trafficking of latent calcium channels. Elife 5: e21143.

57.

Kaeser

Deng

Wang

et al . (2011) RIM proteins tether Ca(2+) channels to presynaptic active zones via a direct PDZ-domain interaction. Cell 144: 282–295.

58.

Katz

Miledi

(1967) A study of synaptic transmission in the absence of nerve impulses. The Journal of Physiology 192: 407–436.

59.

Kimm

Bean

(2014) Inhibition of A-type potassium current by the peptide toxin SNX-482. The Journal of Neuroscience 34: 9182–9189.

60.

Koschak

Reimer

Huber

et al . (2001) Alpha 1D (Cav1.3) subunits can form L-type Ca²⁺ channels activating at negative voltages. Journal of Biological Chemistry 276: 22100–22106.

61.

Koschak

Reimer

Walter

et al . (2003) Cav1.4alpha1 subunits can form slowly inactivating dihydropyridine-sensitive L-type Ca²⁺ channels lacking Ca²⁺-dependent inactivation. The Journal of Neuroscience 23: 6041–6049.

62.

Lee

J-H

Daud

Cribbs

et al . (1999) Cloning and expression of a novel member of the low voltage activated T type calcium channel family. Journal of Neuroscience 19: 1912–1921.

63.

Lee

Tsien

(1983) Mechanism of calcium channel blockade by verapamil, D600, diltiazem and nitrendipine in single dialysed heart cells. Nature 302: 790–794.

64.

Lemke

Welling

Christel

et al . (2008) Unchanged beta-adrenergic stimulation of cardiac l-type calcium channels in CAv1.2 phosphorylation site S1928A mutant mice. Journal of Biological Chemistry 283: 34738–34744.

65.

Llinás

Yarom

(1981) Electrophysiology of mammalian inferior olivary neurones in vitro. Different types of voltage-dependent ionic conductances. The Journal of Physiology 315: 549–567.

66.

Llinás

Sugimori

Lin

J-W

et al . (1989) Blocking and isolation of a calcium channel from neurons in mammals and cephalopods utilizing a toxin fraction (FTX) from funnel-web spider poison. Proceedings of the National Academy of Sciences of the United States of America 86: 1689–1693.

67.

McCleskey

Fox

Feldman

et al . (1987) Omega-conotoxin: Direct and persistent blockade of specific types of calcium channels in neurons but not muscle. Proceedings of the National Academy of Sciences of the United States of America 84: 4327–4331.

68.

Mansergh

Orton

Vessey

et al . (2005) Mutation of the calcium channel gene Cacna1f disrupts calcium signaling, synaptic transmission and cellular organization in mouse retina. Human Molecular Genetics 14: 3035–3046.

69.

Marger

Gelot

Alloui

et al . (2011) T-type calcium channels contribute to colonic hypersensitivity in a rat model of irritable bowel syndrome. Proceedings of the National Academy of Sciences of the United States of America 108: 11268–11273.

70.

Meir

Bell

Stephens

et al . (2000) Calcium channel beta subunit promotes voltage-dependent modulation of α1B by Gβγ. Biophysical Journal 79: 731–746.

71.

Mikami

Imoto

Tanabe

et al . (1989) Primary structure and functional expression of the cardiac dihydropyridine-sensitive calcium channel. Nature 340: 230–233.

72.

Miljanich

(2004) Ziconotide: Neuronal calcium channel blocker for treating severe chronic pain. Current Medicinal Chemistry 11: 3029–3040.

73.

Mintz

Venema

Swiderek

et al . (1992) P-type calcium channels blocked by the spider toxin w-Aga-IVA. Nature 355: 827–829.

74.

Mori

Friedrich

Kim

et al . (1991) Primary structure and functional expression from complementary DNA of a brain calcium channel. Nature 350: 398–402.

75.

Müller

Haupt

Bildl

et al . (2010) Quantitative proteomics of the Cav2 channel nano-environments in the mammalian brain. Proceedings of the National Academy of Sciences of the United States of America 107: 14950–14957.

76.

Neely

Hess

Costigan

et al . (2010) A genome-wide Drosophila screen for heat nociception identifies alpha2delta3 as an evolutionarily conserved pain gene. Cell 143: 628–638.

77.

Newcomb

Szoke

Palma

et al . (1998) Selective peptide antagonist of the class E calcium channel from the venom of the tarantula Hysterocrates gigas. Biochemistry 37: 15353–15362.

78.

Nilius

Hess

Lansman

et al . (1985) A novel type of cardiac calcium channel in ventricular cells. Nature 316: 443–446.

79.

Noda

Shimizu

Tanabe

et al . (1984) Primary structure of electrophorus electricus sodium channel deduced from cDNA sequence. Nature 312: 121–127.

80.

Nowycky

Fox

Tsien

(1985) Three types of neuronal calcium channel with different calcium agonist sensitivity. Nature 316: 440–446.

81.

Opatowsky

Chen

Campbell

et al . (2004) Structural analysis of the voltage-dependent calcium channel beta subunit functional core and its complex with the alpha1 interaction domain. Neuron 42: 387–399.

82.

Page

Canti

Stephens

et al . (1998) Identification of the amino terminus of neuronal Ca²⁺ channel α1 subunits α1B and α1E as an essential determinant of G protein modulation. Journal of Neuroscience 18: 4815–4824.

83.

Patel

Bauer

Nieto-Rostro

et al . (2013) alpha2delta-1 gene deletion affects somatosensory neuron function and delays mechanical hypersensitivity in response to peripheral nerve damage. The Journal of Neuroscience 33: 16412–16426.

84.

Payandeh

Scheuer

Zheng

et al . (2011) The crystal structure of a voltage-gated sodium channel. Nature 475: 353–358.

85.

Pearson

Sutton

Scott

et al . (1995) Characterization of Ca²⁺ channel currents in cultured rat cerebellar granule neurones. Journal of Physiology 482: 493–509.

86.

Peng

Frank

(1989) Activation of GABAB receptors causes presynaptic inhibition at synapses between muscle spindle afferents and motoneurons in the spinal cord of bullfrogs. Journal of Neuroscience 9: 1502–1515.

87.

Perez-Reyes

Cribbs

Daud

et al . (1998) Molecular characterization of a neuronal low-voltage-activated T type calcium channel. Nature 391: 896–900.

88.

Peterson

DeMaria

Yue

(1999) Calmodulin is the Ca²⁺ sensor for Ca²⁺-dependent inactivation of 1-type calcium channels. Neuron 22: 549–558.

89.

Pirone

Kurt

Zuccotti

et al . (2014) alpha2delta3 is essential for normal structure and function of auditory nerve synapses and is a novel candidate for auditory processing disorders. The Journal of Neuroscience 34: 434–445.

90.

Plummer

Logothetis

Hess

(1989) Elementary properties and pharmacological sensitivities of calcium channels in mammalian peripheral neurons. Neuron 2: 1453–1463.

91.

Pragnell

De Waard

Mori

et al . (1994) Calcium channel β-subunit binds to a conserved motif in the I-II cytoplasmic linker of the α₁-subunit. Nature 368: 67–70.

92.

Pragnell

Sakamoto

Jay

et al . (1991) Cloning and tissue-specific expression of the brain calcium channel β-subunit. FEBS Letters 291: 253–258.

93.

Qian

Patriarchi

Price

et al . (2017) Phosphorylation of Ser1928 mediates the enhanced activity of the L-type Ca²⁺ channel Cav1.2 by the beta2-adrenergic receptor in neurons. Science Signaling 10: eaaf9659.

94.

Qin

Platano

Olcese

et al . (1998) Unique regulatory properties of the type 2a Ca²⁺ channel β subunit caused by palmitoylation. Proceedings of the National Academy of Sciences of the United States of America 95: 4690–4695.

95.

Qin

Yagel

Momplaisir

et al . (2002) Molecular cloning and characterization of the human voltage-gated calcium channel α₂δ-4 subunit. Molecular Pharmacology 62: 485–496.

96.

Randall

Tsien

(1995) Pharmacological dissection of multiple types of Ca²⁺ channel currents in rat cerebellar granule neurons. Journal of Neuroscience 15: 2995–3012.

97.

Reuter

(1967) The dependence of slow inward current in Purkinje fibres on the extracellular calcium-concentration. The Journal of Physiology 192: 479–492.

98.

Reuter

(1983) Calcium channel modulation by neurotransmitters, enzymes and drugs. Nature 301: 569–574.

99.

Richards

Butcher

Dolphin

(2004) Calcium channel beta subunits: Structural insights AID our understanding. Trends in Pharmacological Sciences 25: 626–632.

100.

Ringer

(1883) A further contribution regarding the influence of the different constituents of the blood on the contraction of the heart. The Journal of Physiology 4: 29–4223.

101.

Rios

Brum

(1987) Involvement of dihydropyridine receptors in excitation-contraction coupling in skeletal muscle. Nature 325: 717–720.

102.

Ruth

Röhrkasten

Biel

et al . (1989) Primary structure of the β subunit of the DHP-sensitive calcium channel from skeletal muscle. Science 245: 1115–1118.

103.

Saegusa

Kurihara

Zong

et al . (2001) Suppression of inflammatory and neuropathic pain symptoms in mice lacking the N-type Ca²⁺ channel. EMBO Journal 20: 2349–2356.

104.

Schramm

Thomas

Towart

et al . (1983) Novel dihydropyridines with positive inotropic action through activation of Ca²⁺ channels. Nature 303: 535–537.

105.

Scott

Dolphin

(1986) Regulation of calcium currents by a GTP analogue: potentiation of (-)-baclofen-mediated inhibition. Neurosci Lett 69: 59–64.

106.

Serysheva

Ludtke

Baker

et al . (2002) Structure of the voltage-gated L-type Ca²⁺ channel by electron cryomicroscopy. Proceedings of the National Academy of Sciences of the United States of America 99: 10370–10375.

107.

Snutch

Leonard

Gilbert

et al . (1990) Rat brain expresses a heterogeneous family of calcium channels. Proceedings of the National Academy of Sciences of the United States of America 87: 3391–3395.

108.

Soong

Stea

Hodson

et al . (1993) Structure and functional expression of a member of the low voltage-activated calcium channel family. Science 260: 1133–1136.

109.

Starr

TVB

Prystay

Snutch

(1991) Primary structure of a calcium channel that is highly expressed in the rat cerebellum. Proceedings of the National Academy of Sciences of the United States of America 88: 5621–5625.

110.

Striessnig

Ortner

Pinggera

(2015) Pharmacology of L-type calcium channels: Novel drugs for old targets? Current Molecular Pharmacology 8: 110–122.

111.

Strom

Nyakatura

Apfelstedt Sylla

et al . (1998) An L-type calcium-channel gene mutated in incomplete X-linked congenital stationary night blindness. Nature Genetics 19: 260–263.

112.

Takahashi

Seager

Jones

et al . (1987) Subunit structure of dihydropyridine-sensitive calcium channels from skeletal muscle. Proceedings of the National Academy of Sciences of the United States of America 84: 5478–5482.

113.

Tanabe

Beam

Powell

et al . (1988) Restoration of excitation-contraction coupling and slow calcium current in dysgenic muscle by dihydropyridine receptor complementary DNA. Nature 336: 134–139.

114.

Tanabe

Takeshima

Mikami

et al . (1987) Primary structure of the receptor for calcium channel blockers from skeletal muscle. Nature 328: 313–318.

115.

Tang

Gamal El-Din

Payandeh

et al . (2014) Structural basis for Ca²⁺ selectivity of a voltage-gated calcium channel. Nature 505: 56–61.

116.

Tang

Gamal El-Din

Swanson

et al . (2016) Structural basis for inhibition of a voltage-gated Ca²⁺ channel by Ca²⁺ antagonist drugs. Nature 537: 117–121.

117.

Tomita

Chen

Kawasaki

et al . (2003) Functional studies and distribution define a family of transmembrane AMPA receptor regulatory proteins. Journal of Cell Biology 161: 805–816.

118.

Van Petegem

Clark

Chatelain

et al . (2004) Structure of a complex between a voltage-gated calcium channel beta-subunit and an alpha-subunit domain. Nature 429: 671–675.

119.

Walsh

Davies

Butcher

et al . (2009) 3D structure of CaV3.1: Comparison with the cardiac L-type voltage-gated calcium channel monomer architecture. Journal of Biological Chemistry 284: 22310–22321.

120.

Wheeler

Groth

et al . (2012) Ca(V)1 and Ca(V)2 channels engage distinct modes of Ca(2+) signaling to control CREB-dependent gene expression. Cell 149: 1112–1124.

121.

Williams

Feldman

McCue

et al . (1992) Structure and functional expression of α₁, α₂, and β subunits of a novel human neuronal calcium channel subtype. Neuron 8: 71–84.

122.

Wolf

Eberhart

Glossmann

et al . (2003) Visualization of the domain structure of an L-type Ca²⁺ channel using electron cryo-microscopy. Journal of Molecular Biology 332: 171–182.

123.

Yan

et al . (2016) Structure of the voltage-gated calcium channel Cav1.1 at 3.6 A resolution. Nature 537: 191–196.

124.

Lipscombe

(2001) Neuronal Ca_v1.3α₁ L-type channels activate at relatively hyperpolarized membrane potentials and are incompletely inhibited by dihydropyridines. Journal of Neuroscience 21: 5944–5951.

125.

Yang

Ellinor

Sather

et al . (1993) Molecular determinants of Ca²⁺ selectivity and ion permeation in L-type Ca²⁺ channels. Nature 366: 158–161.

126.

Yang

Dai

Yuan

et al . (2016) Loss of beta-adrenergic-stimulated phosphorylation of CaV1.2 channels on Ser1700 leads to heart failure. Proceedings of the National Academy of Sciences of the United States of America 113: E7976–E7985.

Voltage-gated calcium channels: Their discovery,function and importance as drug targets

Abstract

Keywords

Introduction: the importance of Ca2+ entry for function of excitable cells

Identification of multiple subtypes of calcium channel

Identification of N-, P- and R-type calcium currents as distinct from L-type channels

Purification and molecular identification of the calcium channel subtypes

Importance of auxiliary subunits

Elucidation of physiological channel function from knockout mouse studies and genetic mutations

Structural studies

Calcium channel modulation

G-protein modulation

Cyclic AMP-dependent phosphorylation

Future research

Footnotes

Declaration of conflicting interests

Funding

References

Introduction: the importance of Ca²⁺ entry for function of excitable cells