KN-62, A SPECIFIC CA-DEPENDENT PROTEIN-KINASE INHIBITOR, REVERSIBLY DEPRESSES THE RATE OF BEATING OF CULTURED FETAL MOUSE CARDIAC MYOCYTES(+ CALMODULIN)

Effects of KN-62 {1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L- tyros yl]-4-phenylpiperazine}, a specific Ca++/calmodulin (CaM)-dependent pr otein kinase inhibitor, were examined on the rate of spontaneous beati ng and the intracellular Ca++ transient of cultured myocytes from feta l mouse ventricle. KN-62 depressed the rate of beating in a dose-depen dent fashion. Spontaneous beating ceased 10 min after the administrati on of 1 mu M KN-62 and recovered gradually after washing with cultured medium. Addition of KN-04 phenylpiperazinyl)ethyl}-5-isoquinolinsulfo namide; 1 mu M], an analog of KN-62, did not change the rate of beatin g. In the experiment using an intracellular Ca++ fluorescence indicato r, fluo-3, KN-62 depressed the fluo-3 intensity at a systolic phase. T he kinase activity to syntide-2 of Ca++/CaM kinase II purified from th e rabbit heart was inhibited by KN-62, but not by KN-04. Addition of K N-62 inhibited the phosphorylation of phospholamban by Ca++/CaM kinase II in a dose-dependent manner. KN-62 depressed the Ca++-pumping ATPas e activity in the presence of Ca++ and CaM by 32%. These findings indi cate that Ca++/CaM kinase II changes an intracellular Ca++ transient a nd modulates the rate of beating at least in part.