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 isoforms: Cav1.1, Cav1.2, Cav1.3, and 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. They are also found in neurons, and with the help of L-type calcium channels in endocrine cells, they regulate neurohormones and neurotransmitters. They have also been seen to play a role in gene expression, mRNA stability, neuronal survival, ischemic-induced axonal injury, synaptic efficacy, and both activation and deactivation of other ion channels. In cardiac myocytes, the L-type calcium channel passes inward Ca2+ current (ICaL) 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 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. History In 1953, Paul Fatt and Bernard Katz discovered voltage gated calcium channels in crustacean muscle. The channels exhibited different activation voltages and calcium conducting properties and were thus separated into High Voltage Activating channels (HVA) and Low Voltage Activating channels (LVA). After further experimentation, it was found that HVA channels would open to 1,4-dihydropyridine (DHPs). Using DHPs, they found that HVA channels were specific to certain tissues and reacted differently, which led to further categorization of the HVA channels into L-type, P-type, and N-type. L-type calcium channels were peptide sequenced and it was found that there were 4 kinds of L-type calcium channels: α1S (Skeletal Muscle), α1C (Cardiac), α1 D (found in the brain), and α1F (found in the retina). In 2000, after more research was done on α1 subunits in voltage-gated calcium channels, a new nomenclature was