Calcium currents and arrhythmias: Insights from molecular biology

Calcium channels are critical to normal cardiac function. They are involved in the generation and conduction of the action potential and in contractio n. Three surface membrane channels have been identified. The L-type Ca chan nel is most abundant and is responsible for Ca entry into the cell that tri ggers contraction. T-type Ca channels art: most prevalent in the conduction system and are probably involved in automaticity. A newly described TTX-se nsitive calcium current may be important in "boosting" or enhancing conduct ion and contraction. The main intracellular Ca channel resides in the sarco plasmic reticulum and is responsible for the release of the Ca that activat es contraction. Oscillatory behavior of this channel influences the sarcole mmal membrane, causing delayed aftercontractions and arrhythmias such as th ose seen in digoxin toxicity. The on-going molecular characterization of th ese channels will enhance our knowledge of their normal function and dysfun ction in disease stares, leading to the development of new therapeutic agen ts to treat arrhythmias and contractile dysfunction. (C) 2001 by Excerpta M edica, Inc.