L-Type calcium channel

L-Type Calcium Channel

The L-Type calcium channel is a type of voltage-gated calcium channel. 'L' stands for 'long-lasting' referring to the length of activation. This channel is responsible for the excitation-contraction coupling of skeletal, smooth, cardiac muscle, and for aldosterone secretion in adrenal cortex.

Structure

The L-type calcium channel is a complex of multiple proteins with the main alpha subunit forming the ion conducting pore while the auxiliary subunits help to regulate the properties of the channel. The alpha subunit forms the pore through which ions pass into the cell. The alpha subunit is composed of 4 homologous domains (I-IV), each containing 6 transmembrane segments (S1 to S6) for a total of 24 transmembrane segments.

Function

The L-type calcium channel is activated by cell depolarization and conducts the entry of calcium ions, which triggers calcium-induced calcium release (CICR) from the sarcoplasmic reticulum in cardiac and skeletal muscle cells. This leads to muscle contraction. In the adrenal cortex, the release of calcium ions from the L-type calcium channel triggers the secretion of aldosterone, a hormone that regulates blood pressure.

Clinical significance

L-type calcium channels are the target of various pharmacological agents used in the treatment of hypertension such as dihydropyridines, phenylalkylamines, and benzothiazepines, which are classes of calcium channel blockers. These drugs prevent the influx of calcium ions through the L-type channels reducing contractility and conductivity in the heart and vasculature.

See also

• T-type calcium channel
• N-type calcium channel
• P/Q-type calcium channel
• R-type calcium channel