THE NEWLY SYNTHESIZED SELECTIVE CA2+/CALMODULIN DEPENDENT PROTEIN KINASE-II INHIBITOR KN-93 REDUCES DOPAMINE CONTENTS IN PC12H CELLS

We reported that one of the isoquinolinesulfonamide derivatives, KN-62, is a potent and specific inhibitor of Ca2+ calmodulin-dependent protein kinase II (CaMKII) (Tokumitsu, H., Chijiwa, T., Hagiwara, M., Mizutani, A., Terasawa, M. and Hidaka, H. (1990) J. Biol. Chem. 265, 4315-4320). We have now investigated the inhibitory property of a newly synthesized methoxybenzenesulfonamide, KN-93, on CaMKII activity in situ and in vitro. KN-93 elicited potent inhibitory effects on CaMKII phosphorylating activity with an inhibition constant of 0.37 μM but this compound had no significant effects on the catalytic activity of cAMP-dependent protein kinase, Ca2+ phospholipid dependent protein kinase, myosin light chain kinase and Ca2+-phosphodiesterase. KN-93 also inhibited the auto-phosphorylation of both the α- and β-subunits of CaMKII. Kinetic analysis indicated that KN-93 inhibits CaMKII, in a competitive fashion against calmodulin. To evaluate the regulatory role of CaMKII on catecholamine metabolism, we examined the effect of KN-93 on dopamine (DA) levels in PC12h cells. The DA levels decreased in the presence of KN-93. Further, the tyrosine hydroxylase (TH) phosphorylation induced by KCl or acetylcholine was significantly suppressed by KN-93 in PC12h cells while events induced by forskolin or 8-Br-cAMP were not affected. These results suggest that KN-93 inhibits DA formation by modulating the reaction rate of TH to reduce the Ca2+-mediated phosphorylation levels of the TH molecule. © 1991.