Cytochemical localization of adenyl cyclase activity in rat islets of Langerhans

A cytochemical method has been used to investigate the localization of adenyl cyclase activity in A and B cells of isolated rat islets of Langerhans. Adenosine triphosphate was initially utilized as substrate, the pyrophosphate liberated being precipitated by lead ions at its site of production. The specificity of the method was increased by the use of aden-ylyl-imidodiphosphate as an alternative substrate; this adenosine triphosphate analogue was not hydrolyzed by adenosine triphosphatase but provided an effective substrate for adenyl cyclase. Adenyl cyclase activity, which was found to retain its glucagon and fluo-ride sensitivity in glutaraldehyde-fixed tissue, was found exclusively and almost uni-formly in the plasma membranes of A and B cells. Storage granule membrane, incorpo-rat5ed into the plasma membrane during secretion of the granule content by exocytosis, appeared to be devoid of adenyl cyclase activity. There is increasing evidence to suggest that adenosine 3’, 5-cyclic monophosphate (cyclic AMP) may play an important role in the regu-lation of rates of secretion of insulin from th