Effects of hexose pentaacetates on electrical activity and cytosolic Ca2+ in mouse pancreatic islets

Electrical activity of beta-cells and cytosolic Ca2+ concentration ([Ca2+]( i)) were monitored in mouse pancreatic islets exposed to the pentaacetate e sters of alpha-D-glucose, beta-D-galactose and beta-L-glucose, all tested a t 1.7 mM concentration. In the of 5 mM D-glucose, alpha-D-glucose pentaacet ate induced electrical activity and increased [Ca2+](i), whilst beta-D-gala ctose pentaacetate failed to do so. The electrical and cationic response to the D-glucose ester occurred with a delay of between 5 and 10 min, the est er-induced increase in [Ca2+](i) being suppressed in the absence of extrace llular Ca2+. As a rule: beta-L-glucose pentaacetate also failed to evoke bi ophysical responses in the islets exposed to 5 mM D-glucose. However, in th e presence of 10 mM L-leucine the L-glucose ester induced electrical activi ty. These findings, which parallel the insulinotropic action of the same ea ters in rat pancreatic islets reinforce the view that the positive insulino tropic action of selected hexose pentaacetates cannot be attributed to the catabolism of their acetate moiety but, instead, involves a dual mode of ac tion linked to both the metabolism of their carbohydrate moiety and a direc t effect of the ester itself upon a yet unidentified receptor system. Furth ermore, this study provides the first evidence that the latter direct effec t results in the induction of both electrical activity and [Ca2+](i) oscill ations.