Altered intracellular Ca 2+ regulation in pancreatic acinar cells from acute streptozotocin-induced diabetic rats

Abstract

We investigated intracellular Ca 2+ regulation in pancreatic acinar cells from rats with diabetes induced by a single injection of streptozotocin (80 mg/kg). Experiments were performed 2 days and 7 days after the injection of streptozotocin. The density of muscarinic receptors, measured by [ 3H] N-methyl scopolamine binding, was unchanged in 2-day-diabetic rats, but was significantly increased in 7-day-diabetic rats. The percentage of high affinity receptors (R H) and low affinity receptors (R L) determined from the competitive curves with [ 3H] N-methyl scopolamine and carbachol was not change in 2-day-diabetic rats compared to controls, whereas 7-day-diabetic rats showed a decrease in %R H and an increase in %R L. The carbachol-evoked initial peak of intracellular Ca 2+ concentration ([Ca 2+] i) was increased in 2-day-diabetic rats and decreased in 7-day-diabetic rats, compared to controls. In the carbachol-induced sustained phase in [Ca 2+] i, the response in 7-day-diabetic rats was significantly decreased; however, there was no difference between controls and 2-day-diabetic rats. Carbachol (100 μM)-induced [ 3H]inositol 1,3,4-trisphosphate generation was significantly lower in diabetic rats than in the controls. The addition of inositol 1,4,5-trisphosphate (1,4,5-IP 3) significantly increased 45Ca 2+ release from saponin-permeabilized cells in 2-day-diabetic rats, but did not do so in 7-day-diabetic rats. Ca 2+ refilling into the intracellular stores, determined by second cholecystokinin-8 (10 nM) stimulation after 10 μM carbachol stimulation, was increased in 2-day-diabetic rats and decreased in 7-day-diabetic rats. These observations indicate that the alterations in intracellular Ca 2+ regulation accompanied by changes in transmembrane signaling occur in the earlier stage of the diabetic state. The findings also suggest that the increase in the carbachol-evoked [Ca 2+] i peak in 2-day-diabetic rats is related predominantly to the higher sensitivity of 1,4,5-IP 3-sensitive Ca 2+ stores and the increase in the capacity of Ca 2+ refilling in these animals, whereas the reduction in the [Ca 2+] i peak in 7-day-diabetic rats appears to be related to the essential decrease in receptor-mediated 1,4,5-IP 3 generation and the decrease in Ca 2+ refilling capacity.