Difference in mechanism between glyceraldehyde- and glucose-induced insulin secretion from isolated rat pancreatic islets

Abstract

The effects of D-glyceraldehyde and glucose on islet function were compared in order to investigate the difference between them in the mechanism by which they induce insulin secretion. The stimulation of insulin secretion from isolated rat islets by 10 mM glyceraldehyde was not completely inhibited by either 150 μM diazoxide (an opener of ATP-sensitive K+ channels) or 5 μM nitrendipine (an L-type Ca2+-channel blocker), whereas the stimulation of insulin secretion by 20 mM glucose was completely inhibited by either drug. The insulin secretion induced by glyceraldehyde was less augmented by 100 μM carbachol (a cholinergic agonist) than that induced by glucose. The stimulation of myoinositol phosphate production by 100 μM carbachol was more marked in islets incubated with the hexose than with the triose. The content of glyceraldehyde 3-phosphate, a glycolytic intermediate, in islets incubated with glyceraldehyde was far higher than that in islets incubated with glucose, whereas the ATP content in islets incubated with the triose was significantly lower than that in islets incubated with the hexose. These results suggest that glyceraldehyde not only mimics the effect of glucose on insulin secretion but also has the ability to cause the secretion of insulin without the influx of Ca2+ through voltage-dependent Ca2+ channels. The reason for the lower potency of the triose than the hexose in stimulating insulin secretion is also discussed.