Ca2+/Calmodulin‐Dependent Protein Kinase II Inhibitor KN‐62 Inhibits Adrenal Medullary Chromaffin Cell Functions Independent of Its Action on the Kinase

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Abstract
KN‐62, an inhibitor of Ca2+/calmodulin‐dependent protein kinase II (CaM kinase II), inhibited significantly catecholamine secretion and tyrosine hydroxylase activity stimulated by acetylcholine in cultured bovine adrenal medullary cells. KN‐62, however, showed an additional inhibitory effect on acetylcholine‐induced 45Ca2+ influx, which is essential for functional responses. Carbachol‐stimulated 22Na+ influx, veratridine‐induced 22Na+ influx, and 56 mM K+‐evoked 45Ca2+ influx were also attenuated by KN‐62. Inhibitions by KN‐62 of these ion influxes were correlated closely with those of catecholamine secretion. KN‐04, which is a structural analogue of KN‐62 but does not inhibit CaM kinase II activity, elicited inhibitory effects on the three kinds of stimulant‐evoked ion influxes with an inhibitory potency similar to KN‐62. These results suggest that KN‐62 inhibits catecholamine secretion and tyrosine hydroxylase activation due to mainly its ion channel blockade on the plasma membrane rather than the inhibition of CaM kinase II activity in the cells.

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