L-type calcium channel
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The L-type calcium channel (also known as the DHP receptor)is part of the high-voltage activated family of voltage-dependent calcium channel. "L" stands for long-lasting referring to the length of activation. L-type calcium channels are responsible for 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 sarcoplamic reticulum by activating Ryanodine Receptor 2 (RyR2) (calcium-induced-calcium-release). 
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 vessels (the dihydropyridines, like nifedipine).
In skeletal muscle, there is a very high concentration of L-type calcium channels, situated in the T-tubules. Muscle depolarization results in large gating currents, but anomalously low calcium flux, which is now explained by the very slow activation of the ionic currents. For this reason, little or no Ca2+ passes across the T-tubule membrane 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.
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- "Voltage-Gated Calcium Channels". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology.
- L-Type Calcium Channel at the US National Library of Medicine Medical Subject Headings (MeSH)