Role of calcium in suppression of glucagon release from isolated diabetic rat pancreata.

To investigate the role of extracellular Ca2+ (Ca2+) in suppression of glucagon release in diabetic animals, pancreata were isolated from streptozotocin-diabetic rats and perfused with a 15 mM glucose solution containing one of the following: (1) Ca2+ 2.1 mM and insulin 22 microU/ml, (2) Ca2+ 2.1 mM and insulin 110 microU/ml, (3) Ca2+ 2.1 mM and insulin (-) or (4) Ca2+ 0.2 mM and insulin 110 microU/ml. Although perfusion with 22 microU/ml of insulin did not alter glucagon release, perfusion with 110 microU/ml of insulin in the presence of Ca2+ and glucose significantly reduced the release of glucagon from 1.9 +/- 0.3 ng/min to 1.2 +/- 0.3 ng/min for the first 3 min. The absence of insulin enhanced glucagon release from the baseline level of 1.0 +/- 0.1 ng/min to 1.6 +/- 0.3 ng/min at 11 min and to 1.4 +/- 0.2 ng/min at 21 min. Deprivation of Ca2+ in the perfusate also enhanced glucagon release from the baseline level of 0.8 +/- 0.1 ng/min to 1.2 +/- 0.3 ng/min for the first 4 min. It is concluded that insulin suppresses glucagon release and Ca2+ is needed for the suppression of glucagon release in the presence of both insulin and glucose in streptozotocin-diabetic rat pancreata.