The Ca++/calmodulin-dependent protein kinase II inhibitors KN62 and KN93, and their inactive analogues KN04 and KN92, inhibit nicotinic activation of tyrosine hydroxylase in bovine chromaffin cells.

The possible role of Ca++/calmodulin-dependent protein kinase II (CAM-K-II) in the nicotinic activation of tyrosine hydroxylase in intact cultured bovine adrenal chromaffin cells has been investigated. Over the concentration range 3-30 microM, KN62, a specific CAM-K-II inhibitor, inhibited basal tyrosine hydroxylase activity and the activity stimulated by nicotine or K+ depolarisation. KN04, a structural analogue of KN62 which does not inhibit CAM-K-II, produced an identical concentration-dependent inhibition of basal and nicotine-stimulated tyrosine hydroxylase activity. Another CAM-K-II inhibitor, KN93, also inhibited nicotine and K+ stimulation of tyrosine hydroxylase activity; however, an inactive analogue of KN93, KN92, mimicked these effect. The results suggest that the inhibition of nicotine- and K+-stimulated tyrosine hydroxylase activity by KN62 and KN93 is not due to their ability to inhibit CAM-K-II.