Metabolic concomitants in pure, pancreatic beta cells during glucose-stimulated insulin secretion

The role of the redox potential in insulin secretion by beta cells stimulated with high glucose was investigated using an in vitro pancreas perfusion system. To assess glycolytic flux the sum of fructose-1,6-P2 + triose-P was determined in pure beta cells microdissected from lyophilized sections of the isolated perfused pancreas quick frozen during the early insulin secretory response. L-Glycerol 3-phosphate and dihydroxyacetone phosphate were measured as indicators of the free cytosolic [NAD+]/[NADH] ratio and NADH and NADPH were also measured. Fructose-1,6-P2 + triose-P was increased in beta cells simultaneously with the onset of insulin secretion indicating an increase in glucose metabolism had occurred. The ratio of [dihydroxyacetone phosphate]/[L-glycerol 3-phosphate] increased simultaneously with the onset of insulin secretion. NADH content increased only after initiation of insulin secretion and NADPH levels remained unchanged during the early secretory response to high glucose. These data contradict the hypothesis that insulin secretion is triggered by a more reduced cytosolic redox state and instead indicate that insulin secretion is initiated by other metabolic coupling factor(s) generated in beta cells stimulated by high glucose.