MUSCARINIC ACTIVATION OF CA2+ CALMODULIN-DEPENDENT PROTEIN-KINASE-II IN PANCREATIC-ISLETS - TEMPORAL DISSOCIATION OF KINASE ACTIVATION AND INSULIN-SECRETION/

We have demonstrated previously that glucose activates the multifuncti onal Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) in is olated rat pancreatic islets in a manner consistent with a role of thi s enzyme in the regulation of insulin secretion [Wenham, Landt and Eas om (1994) J. Biol. Chem. 269, 4947-4952]. In the current study, the mu scarinic agonist, carbachol, has been shown to induce the conversion o f CaM kinase II into a Ca2+-independent, autonomous form indicative of its activation. Maximal activation (2-fold) was achieved by 15 s, fol lowed by a rapid return to basal levels by 1 min. This response was pr imarily the result of the mobilization of Ca2+ from intracellular stor es since it was not affected by a concentration (20 mu M) of verapamil that completely prevented the activation of CaM kinase II by glucose. Surprisingly, carbachol added prior to, or simultaneously with, gluco se attenuated nutrient activation of CaM kinase II. This effect was mi micked by cholecystokinin-8 (CCK-8) and thapsigargin, suggesting its m ediation by phospholipase C and the mobilization of intracellular Ca2. In contrast, carbachol, CCK-8 and thapsigargin markedly potentiated glucose (12 mM)-induced insulin secretion. These results suggest that CaM kinase II activation can be temporally dissociated from insulin se cretion but do not exclude the potential dependence of insulin exocyto sis on CaM kinase II-mediated protein phosphorylation.