<P> Voltage - dependent calcium channels ( VDCCs ) 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 . </P>
<P> Voltage - dependent calcium channels ( VDCCs ) 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 . </P>
where are the calcium-voltage gated channels located in the neuron
where are the calcium-voltage gated channels located in the neuron
membrane
membrane