REGULATION OF MYOCARDIAL CALCIUM CHANNELS BY CYCLIC-AMP METABOLISM

AMP-dependent phosphorylation of the Ca-channel results in an increase of the mean open probability of the individual Ca-channels and, thus, of the macroscopic Ca current. Modulation of cAMP concentration can t ake place at the level of adenylyl cyclases or cAMP phosphodiesterases . Of major interest is the fact that the activity of two different for ms of phosphodiesterases is controlled by the level of intracellular c GMP. Thus, cAMP metabolism is intimately associated with cGMP metaboli sm, and both determine the degree of cAMP-dependent phosphorylation of cardiac Ca-channels. This brief discussion will focus on these two le vels of control and their relative importance in the cAMP-dependent re gulation of myocardial Ca-channels.