CELLULAR-LOCALIZATION OF CALMODULIN-DEPENDENT PROTEIN-KINASE-I AND PROTEIN-KINASE-II TO A-CELLS AND D-CELLS OF THE ENDOCRINE PANCREAS

Ca2+/calmodulin-dependent protein kinases I and II, initially identifi ed in brain on the basis of their ability to phosphorylate synapsin I, have been implicated in the regulation of Ca2+-dependent synaptic neu rosecretion. Specific recombinant and synthetic peptide antibodies wer e used to examine the distribution of CaM kinases I and II in the rat pancreas and other tissues. The CaM kinase I antibodies detected a dou blet of cytosolic proteins of similar to 38 and similar to 42 kD by im munoblot. CaM kinase I was observed in glucagon-containing A-cells at the periphery of the islet of Langerhans but had little or no overlap with pancreatic polypeptide or somatostatin cells. In contrast, CaM ki nase II was localized to somatostatin-containing D-cells. CaM kinase I co-localized with glucagon secretory granules. CaM kinase II was not associated with the somatostatin granule but rather was enriched in ar eas of the cells that contained relatively little somatostatin. Becaus e glucagon secretion is Ca2+-dependent, it is attractive to speculate that CaM kinase I may play a regulatory role in glucagon secretion. Gl ucagon and somatostatin cells both utilize intracellular Ca2+ for sign aling. Therefore, specific CaM kinases may act as effecters of Ca2+ in these different cell types.