Voltage-dependent calcium channel

Voltage-dependent calcium channels (VDCC) are a group of voltage-gated ion channels found in the membrane of excitable cells (e.g., muscle, glial cells, neurons, etc.) with a permeability to the calcium ion Ca. These channels are slightly permeable to sodium ions, so they are also called Ca-Na channels, but their permeability to calcium is about 1000-fold greater than to sodium under normal physiological conditions. At physiologic or resting membrane potential, VDCCs are normally closed. They are activated (i.e., opened) at depolarized membrane potentials and this is the source of the "voltage-dependent" epithet. The concentration of calcium (Ca ions) is normally several thousand times higher outside of the cell than inside. Activation of particular VDCCs allows Ca to rush into the cell, which, depending on the cell type, results in activation of calcium-sensitive potassium channels, muscular contraction, excitation of neurons, up-regulation of gene expression, or release of hormones or neurotransmitters. VDCCs have been immunolocalized in the zona glomerulosa of normal and hyperplastic human adrenal, as well as in aldosterone-producing adenomas (APA), and in the latter T-type VDCCs correlated with plasma aldosterone levels of patients. Excessive activation of VDCCs is a major component of excitotoxicity, as severely elevated levels of intracellular calcium activates enzymes which, at high enough levels, can degrade essential cellular structures.