A calcium channel is an ion channel which shows selective permeability to calcium ions. It is sometimes synonymous with voltage-gated calcium channel,[1] although there are also ligand-gated calcium channels.[2]
The following tables explain gating, gene, location and function of different types of calcium channels, both voltage and ligand-gated.
Main article: voltage-gated calcium channel |
Type | Voltage | α1 subunit (gene name) | Associated subunits | Most often found in |
L-type calcium channel ("Long-Lasting" AKA "DHP Receptor") | HVA (high voltage activated) | Cav1.1 (CACNA1S) Cav1.2 (CACNA1C) Cav1.3 (CACNA1D) Cav1.4 (CACNA1F) |
α2δ, β, γ | Skeletal muscle, smooth muscle, bone (osteoblasts), ventricular myocytes** (responsible for prolonged action potential in cardiac cell; also termed DHP receptors), dendrites and dendritic spines of cortical neurons |
N-type calcium channel ("Neural"/"Non-L") | HVA (high-voltage-activated) | Cav2.2 (CACNA1B) | α2δ/β1, β3, β4, possibly γ | Throughout the brain and peripheral nervous system. |
P-type calcium channel ("Purkinje") /Q-type calcium channel | HVA (high voltage activated) | Cav2.1 (CACNA1A) | α2δ, β, possibly γ | Purkinje neurons in the cerebellum / Cerebellar granule cells |
R-type calcium channel ("Residual") | intermediate-voltage-activated | Cav2.3 (CACNA1E) | α2δ, β, possibly γ | Cerebellar granule cells, other neurons |
T-type calcium channel ("Transient") | low-voltage-activated | Cav3.1 (CACNA1G) Cav3.2 (CACNA1H) Cav3.3 (CACNA1I) |
neurons, cells that have pacemaker activity, bone (osteocytes), thalamus (thalamus) |
Type | Gated by | Gene | Location | Function |
IP3 receptor | IP3 | ITPR1, ITPR2, ITPR3 | ER/SR | Releases calcium from ER/SR in response to IP3 by e.g. GPCRs[4] |
Ryanodine receptor | dihydropyridine receptors in T-tubules and increased intracellular calcium (Calcium Induced Calcium Release - CICR) | RYR1, RYR2, RYR3 | ER/SR | Calcium-induced calcium release in myocytes[4] |
Two-pore channel | Nicotinic acid adenine dinucleotide phosphate (NAADP) | TPCN1, TPCN2 | endosomal/lysosomal membranes | NAADP-activated calcium transport across endosomal/lysosomal membranes[5] |
Cation channels of sperm | Calcium (CICR) | PKD2 family | sperm (specifically flagella) | Non-selective calcium-activated cation channel directing sperm in female reproductive tract[6] |
store-operated channels | indirectly by ER/SR depletion of calcium[4] | ORAI1, ORAI2, ORAI3 | plasma membrane | Provides calcium signaling to the cytoplasm[7] |
L-type calcium channel blockers are used to treat hypertension. In most areas of the body, depolarization is mediated by sodium influx into a cell; changing the calcium permeability has little effect on action potentials. However, in many smooth muscle tissues, depolarization is mediated primarily by calcium influx into the cell. L-type calcium channel blockers selectively inhibit these action potentials in smooth muscle which leads to dilation of blood vessels; this in turn corrects hypertension.[8]
T-type calcium channel blockers are used to treat epilepsy. Increased calcium conductance in the neurons leads to increased depolarization and excitability. This leads to a greater predisposition to epileptic episodes. Calcium channel blockers reduce the neuronal calcium conductance and reduce the likelihood of experiencing epileptic attacks.[9]