Conversion to Ca(2+)-independent form of Ca2+/calmodulin protein kinase II in rat pancreatic acini.

CCK rapidly converted Ca2+/calmodulin kinase II (CaMK II) to a Ca(2+)-independent form with peak action at 30 sec followed by decline to the basal level at 10 min. The threshold concentration of CCK for this action was 30 pM and maximum effect occurred at 1 nM, which induced a 6-10-fold increase. Bombesin and carbachol similarly induced CaMK II autonomous activity, whereas secretin and JMV 180 did not. Ionomycin induced a more stable elevation of CaMK II autonomous activity and the intracellular Ca2+ chelator, BAPTA/AM, blocked the effect of CCK. In conclusion, pancreatic CaMK II is rapidly activated by a large increase in [Ca2+]i generated by either stimulation of phosphatidylinositol pathway or by an influx of extracellular Ca2+.