Channel name | CaV2.2 |
Description | Voltage-gated calcium channel α1 subunit |
Other names | N-type, α1B; rbB-I, rbB-II (in rat),1,2 BIII (in rabbit)3 |
Molecular information | Human: 2339aa, M94172, 2237aa, M94173,4 chr. 9q34, CACN1B |
| Rat: 2336aa, M929051 |
| Mouse: 2329aa, NM007579, NP031605 |
Associated subunits | α2δ/β1, β3, β4,5 possibly γ |
Functional assays | Voltage-clamp, patch-clamp, calcium imaging, neurotransmitter release, 45Ca uptake into synaptosomes |
Current | ICa,N |
Conductance | 20pS (bullfrog sympathetic neurones)6; 14.3pS (rabbit BIII cDNA in skeletal muscle myotubes)3 |
Ion selectivity | Ba2+ > Ca2+ |
Activation | Va = +7.8 mV, τa = 3 ms at +10 mV (human α1B/α2δ/β1-3 in HEK293 cells, 15 mM Ba2+ charge carrier)4,7; Va = +9.7 mV, τa = 2.8 ms at +20 mV (rat α1B-II/β1b, in Xenopus oocytes, 40 mM Ba2+ charge carrier)2 |
Inactivation | Vh = –61 mV, τh ∼200 ms at +10 mV (human α1B/α2δ/β1-3 in HEK293 cells, 15 mM Ba2+ charge carrier)4,7; Vh = –67.5 mV; τh = 112 ms at +20 mV (rat α1B-II/β1b in Xenopus oocytes, 40 mM Ba2+)2 |
Activators | None |
Gating modifiers | None |
Blockers | ω-conotoxin GVIA (1–2 μM, irreversible block), ω-conotoxin MVIIA (SNX-111, Ziconotide/Prialt), ω-conotoxin MVIIC8; other blockers include piperidines, substituted diphenylbutylpiperidines, long alkyl chain molecules, aliphatic monoamines, tetrandine, gabapentin, peptidylamines, volatile anesthetics, the peptide toxins SNX-325 and DW13.3, as well as the ω-conotoxins SVIA, SVIB, and CVID20,21,22,23,24,25,26,27,28,29,30a,30b,30c,30d,30e,31,32,33,34 |
Radioligands | [125I]ω-conotoxin GVIA (Kd = 55 pM, human α1B/α2δ/β1-3 in HEK293 cells)4 |
Channel distribution | Neurons (presynaptic terminals, dendrites, cell bodies)9 |
Physiological functions | Neurotransmitter release in central and sympathetic neurons10; sympathetic regulation of the circulatory system11,35; activity and vigilance state control36; sensation and transmission of pain (see “Pharmacological significance” and “Comments”) |
Mutations and pathophysiology | Differing reports exist: mice lacking a functional CaV2.2 gene exhibit a normal life span and no detectable behavioral modifications compared with wild type but possess an increase in basal mean atrial pressure and other functional alterations to the sympathetic nervous system11–however, in a different study, approximately 1/3 of the mice lacking a functional CaV2.2 gene did not survive to weaning, but surviving animals were normal except for a decrease in anxiety-related behavior and a suppression of inflammatory and neuropathic pain responses12; no point mutations in the native CaV2.2. gene have been reported to date |
Pharmacological significance | In rats, intrathecal administration of ω-conotoxin GVIA or ω-conotoxin MVIIA shows strong effects on inflammatory pain, postsurgical pain, thermal hyperalgesia, and mechanical allodynia13,14,15; in humans, intrathecal administration of SNX-111 (Ziconotide/Prialt, synthetic ω-conotoxin MVIIA) to patients unresponsive to intrathecal opiates significantly reduced pain scores and in a number of specific instances resulted in relief after many years of continuous pain16 |
Comments | In case studies, Ziconotide/Prialt has been examined for usefulness in the management of intractable spasticity following spinal cord injury in patients unresponsive to baclofen and morphine17; side effects of intrathecal administration of Ziconotide/Prialt include nystagmus, sedation, confusion, auditory and visual hallucinations, severe agitation, and unruly behavior18; intravenous administration of Ziconotide to humans results in significant orthostatic hypotension19; identified regions of alternative splicing include the domain I-II linker, domain II-III linker, IIIS3-IIIS4, IVS3-IVS4, and the carboxyl terminus1,2,3,4,37,38,39; splicing affects a number of channel properties, including current-voltage relations and kinetics, and is associated with cell-specific expression–in particular, expression of the e37a splice isoform in dorsal root ganglia correlates with a subset of nociceptive neurons40,41,42; alternative splicing also alters interactions with intracellular synaptic proteins such as Mint1, CASK, syntaxin, and SNAP-2543,44,45 |