Modulation of Calcium Channels in Cultured Cardiac Cells by Isoproterenol and 8-Bromo-cAMP

The central role played by Ca + + in the regulation of many cellular functions is widely appreciated, and the field centering around this problem is continuously growing. An important aspect of cell regulation by Ca + + is the fact that the free intracellular Ca + + con-centration (Ca + +i) can fluctuate over several orders of magnitude. In many cells, particularly in muscle and neurons, an increase in Ca++a is triggered by depolarization of the cell membrane. It has long been recognized that the Ca + + conductance (gca) of these cells is greatly increased uring excitation (for reviews, see Reuter 1973; Hagiwara and Byerly 1981; Tsien 1983) and that this contributes to the increase in Ca + +, The rise in gca during an action potential has commonly been described by the formalism suggested