A selective Ca2+/calmodulin-dependent protein kinase II inhibitor, KN-62, inhibits the enhanced phosphorylation and the activation of tyrosine hydroxylase by 56 mM K+ in rat pheochromocytoma PC12h cells.

Involvement of Ca2+/calmodulin-dependent protein kinase II (Ca2+/CaM-kinase II) on the phosphorylation of tyrosine hydroxylase (TH, EC.1.14.16.2) in rat pheochromocytoma, PC12h cells was examined using KN-62, 1-[N,O-Bis(5-isoquinolinsulfonyl)-N-methyl-L-tyrosyl]-4-phenylpipe razine, a selective inhibitor of Ca2+/CaM-kinase II. Both the enhanced phosphorylation of TH and the activated L-3,4-dihydroxyphenylalanine (DOPA) formation in the high K+ depolarization were inhibited by 10 microM KN-62. After incubation of PC12h cells with 10 microM KN-62 for 1 hr, the activation of TH with 3 min incubation of 56 mM K+ was reduced to the basal activity. However, KN-62 did not directly affect the activity of purified rat TH at pH 6.0 or 7.0. These results indicate that Ca2+/CaM-kinase II phosphorylates and activates TH of PC12h cells in the high K+ depolarization.