Résumé
Hormonal regulation of cardiac inotropism is often correlated with modification of the L -type Ca-channel current. Among severa! regulatory pathways that control Ca-channel activity, the best described one is the cAMP cascade. Cyclic AMP-dependent phosphorylation of the Ca-channel results in an increase of the mean open probability for individual Ca-channels, and, thus, of the macroscoplc Ca-current. Modulation of cAMP concentration can take place at the level of adenylyl cyclases or cAMP phosphodiesterases. Of major interest is the fact that the activity of two different forms of phosphodiesterases is controlled by the level of intracellular cGMP. Thus, cAMP metabolism is intimately associated with cGMP metabolism, and both determine the degree of cAMP-dependent phosphorylation of cardiac Ca-channels. This briel discussion will focus on these two levels of control and their relative importance for the cAMP-dependent regulation of myocardial Ca-channels.