Carbachol restores insulin release in diabetic GK rat islets by mechanisms largely involving hydrolysis of diacylglycerol and direct interaction with the exocytotic machinery

In several models of insulin resistance, cholinergically induced insulin secretion is augmented. We studied here whether this also is present in the spontaneously diabetic GK (Goto-Kakizaki) rat pancreas. Using carbachol (50 mu mol/L), enhanced insulin release was elicited in perfused pancreas under normal or depolarized conditions in GK compared with control rats at 3.3 mmol/L glucose (p < 0.03). Carbachol fully normalized insulin secretion in GK rats at 16.7 mmol/L glucose through an effect abolished by atropine. Similarly, direct stimulation of protein kinase C (PKC) with the DAG-permeable compound 1-oleoyl-2-acetyl-sn-glycerol (OAG, 300 mol/L) induced more pronounced insulin release in GK islets than in control islets. The diacylglycerol (DAG) lipase inhibitor RHC-80267 (35 mu mol/L) significantly reduced carbachol effects in control and GK islets, but had no effect on GAG-induced insulin release. The enhanced insulinotropic effects of carbachol in GK islets was not accompanied by increased cyclic adenosine monophosphate (cAMP) or arachidonic acid (AA) formation in GK when compared with control islets, In conclusion, cholinergic stimulation induced enhanced insulin release in diabetic GK islets. This is largely mediated through mechanisms involving hydrolysis of DAG to AA and interaction with exocytotic steps of insulin release.