L-type calcium channel

The L-type calcium channel (also known as the dihydropyridine channel, or DHP channel) is part of the high-voltage activated family of voltage-dependent calcium channel.'L' stands for long-lasting referring to the length of activation. This channel has four subunits (Cav1.1, Cav1.2, Cav1.3, Cav1.4). The L-type calcium channel (also known as the dihydropyridine channel, or DHP channel) is part of the high-voltage activated family of voltage-dependent calcium channel.'L' stands for long-lasting referring to the length of activation. This channel has four subunits (Cav1.1, Cav1.2, Cav1.3, Cav1.4). L-type calcium channels are responsible for the excitation-contraction coupling of skeletal, smooth, cardiac muscle, and for aldosterone secretion in endocrine cells of the adrenal cortex. In cardiac myocytes, the L-type calcium channel passes inward Ca2+ current and triggers calcium release from the sarcoplasmic reticulum by activating ryanodine receptor 2 (RyR2) (calcium-induced-calcium-release). Phosphorylation of these channels increases their permeability to calcium and increases the contractility of their respective cardiac myocytes. L-type calcium channel blocker drugs are used as cardiac antiarrhythmics or antihypertensives, depending on whether the drugs have higher affinity for the heart (the phenylalkylamines, like verapamil), or for the blood vessels (the dihydropyridines, like nifedipine). In skeletal muscle, there is a very high concentration of L-type calcium channels, situated inthe T-tubules. Muscle depolarization results in large gatingcurrents, but anomalously low calcium flux, which is nowexplained by the very slow activation of the ionic currents. Forthis reason, little or no Ca2+ passes across the T-tubulemembrane during a single action potential. Like most voltage-gated ion channels, the α-subunit is composed of 4 subunits. Each subunit is formed by 6 alpha-helical, transmembrane domains that cross the membrane (numbered S1-S6). The S1-S4 subunits make up the voltage sensor, while S5-S6 subunits make up the selectivity filter.