Acalcium channel is anion channel which shows selective permeability tocalcium ions. It is sometimes synonymous withvoltage-gated calcium channel,[1] which are a type of calcium channel regulated by changes inmembrane potential. Some calcium channels are regulated by the binding of aligand.[2][3] Other calcium channels can also be regulated by both voltage and ligands to provide precise control over ion flow. Some cation channels allow calcium as well as other cations to pass through the membrane.
Calcium channels can participate in the creation ofaction potentials across cell membranes. Calcium channels can also be used to release calcium ions assecond messengers within the cell, affecting downstream signaling pathways.
The following tables explain gating, gene, location and function of different types of calcium channels, both voltage and ligand-gated.
| 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 thebrain 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 /Cerebellargranule cells |
| R-type calcium channel ("Residual") | intermediate-voltage-activated | Cav2.3 (CACNA1E) | α2δ, β, possibly γ | Cerebellargranule cells, other neurons |
| T-type calcium channel ("Transient") | low-voltage-activated | Cav3.1 (CACNA1G) Cav3.2 (CACNA1H) Cav3.3 (CACNA1I) | Cells that havepacemaker activity in heart, neurons, thalamus (thalamus), bone (osteocytes) |
| 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 inT-tubules and increased intracellular calcium (Calcium Induced Calcium Release - CICR) | RYR1, RYR2, RYR3 | ER/SR | Calcium-induced calcium release inmyocytes[4] |
| Two-pore channel | Nicotinic acid adenine dinucleotide phosphate (NAADP) | TPCN1, TPCN2 | endosomal/lysosomal membranes | NAADP-activated calcium transport across endosomal/lysosomal membranes[5] |
| store-operated channels[6] | indirectly byER/SR depletion of calcium[4] | ORAI1, ORAI2, ORAI3 | plasma membrane | Provides calcium signaling to the cytoplasm[7] |
There are several cation channel families that allow positively charged ions including calcium to pass through. These includeP2X receptors,Transient Receptor Potential (TRP) channels,Cyclic nucleotide-gated (CNG) channels,Acid-sensing ion channels, andSOC channels.[8] These channels can be regulated by membrane voltage potentials, ligands, and/or other cellular conditions.Cat-Sper channels, found in mammalian sperm, are one example of this as they are voltage gated and ligand regulated.[9]
L-typecalcium channel blockers are used to treathypertension. 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.[10]
T-typecalcium channel blockers are used to treatepilepsy. 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.[11]