EFFECTS OF CHOLINERGIC AGONISTS ON DIACYLGLYCEROL AND INTRACELLULAR CALCIUM LEVELS IN PANCREATIC BETA-CELLS

We have studied the effects of cholinergic agonists on the rates of in sulin release and the concentrations of diacylglycerol (DAG) and intra cellular free Ca2+ ([Ca2+]i) in the beta-cell line MIN6. Insulin secre tion was stimulated by glucose, by glibenclamide and by bombesin. In t he presence of glucose, both acetylcholine (ACh) and carbachol (CCh) p roduced a sustained increase in the rate of insulin release which was blocked by EGTA or verapamil. The DAG content of MIN6 beta-cells was n ot affected by glucose. Both CCh and ACh evoked an increase in DAG whi ch was maximal after 5 min and returned to basal after 30 min; EGTA ab olished the cholinergic-induced increase in DAG. ACh caused a transien t rise in [Ca2+]i which was abolished by omission of Ca2+ or by additi on of devapamil. Thus, cholinergic stimulation of beta-cell insulin re lease is associated with changes in both [Ca2+]i and DAG. The latter c hange persists longer than the former and activation of protein kinase C and sensitization of the secretory process to Ca2+ may underlie the prolonged effects of cholinergic agonists on insulin release. However , a secretory response to CCh was still evident after both [Ca2+]i and DAG had returned to control values suggesting that additional mechani sms may be involved.