Effect of insulin on acetylcholine-evoked amylase release and calcium mobilization in streptozotocin-induced diabetic rat pancreatic acinar cells

This article investigated the effect of acetylcholine (ACh) on amylase secretion and cellular calcium homeostasis [Ca2+](i) in streptozotocin (STZ; 60 mg kg(-1), intraperitoneally)-induced diabetic rats compared to age-matched controls in an attempt to understand the cellular mechanism of exocrine pancreatic insufficiency. ACh-evoked marked dose-dependent increases in amylase release from isolated pancreatic acini and acinar cells in healthy control rats. In diabetic acini and acinar cells, the ACh-evoked amylase release was significantly (P < 0.05) reduced compared to healthy acini and acinar cells. Insulin (10(-6) M) stimulated amylase release in both control and diabetic acini and acinar cells but with a much reduced effect in diabetic tissues. Combining insulin with ACh had no significant effect on amylase release compared to the effect of ACh alone. In fura-2 loaded pancreatic acinar cells of normal rats, ACh (10(-5) M) evoked a large initial rise (peak) in [Ca2+](i) followed by a decline into a plateau phase. This effect of ACh was significantly (p < 0.05) reduced in fura-2 loaded diabetic acinar cells. In control cells, insulin had no significant effect on either basal or ACh evoked [Ca2+](i), compared to the effect of ACh alone. In contrast, in diabetic acinar cells, insulin significantly (P < 0.05) attenuated the effect of ACh. In a normally free extracellular Ca2+ medium [Ca2+](0) containing 1 mM EGTA, the kh-evoked [Ca2+](i) in normal healthy fura-2 loaded acini was similar to the response obtained with ACh in fura-2 loaded diabetic acini. Together, the results indicated that exocrine pancreatic insufficiency is associated with decreased [Ca2+](i) due to less Ca2+ released from internal stores and less Ca2+ entering the cell from the extracellular medium.