Modulation Of Calcium Channels in Cardiac Cells by Neurotransmitters
Voltage dependent Ca channels are widely distributed in excitable cells, and important cellular functions are regulated by Ca ions moving through such channels. Adrenergic neurotransmitter effects on Ca currents, Ica, in cardiac cells have served as prime examples of modulation of voltagegated ion channels. Recently it has become possible to analyze molecular events Involved in Ca channel modulation. Ca channels are activated by changes in membrane potential. The probability, po, steeply with depolarization. Anallysis of the gating kinetics of Ca channels in the presence of catecholamines or 8-bromo-cAMP showed (a) an increase In the mean open time of Ca channels, (b) a decrease in closed times between bursts of openings, and (c) a reduction in failures of a channel to open upon repetitive depolarizations. These kinetic changes result in an overall increase in po. The number of functional channels, Nf, may also be increased, while the single channel current, i, is not affected. These results explain the increase of ICa = Nf.po.i. cAMP-dependent phosphorylatlon of the channels is a likely intermediate step in this modulation.
KeywordsKinetic Transition Single Channel Current Kinetic Change Functional Channel Important Cellular Function
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