Single cell analysis of pyruvate oxidation in the intact isolated islet revealed by two-photon microscopy

It is generally accepted that glucose-stimulated insulin secretion from the pancreatic beta cell is proportional to the rate of glucose metabolism, and the ATP produced is linked to the secretory machinery via ATP sensitive potassium channels. However, the rote of mitochondrial metabolism seems paradoxical. Secretion induced by glycolytic substrates is inhibited when mitochondrial ATP formation is disrupted by' electron transport inhibitors or uncouplers, However, pyruvate does not cause secretion even though it is rapidly oxidized by islets. We suspected heterogeneous pyruvate oxidation among beta and non-beta cell populations within the islet. NAD(P)It imaging via two-photon-excitation microscopy provides a new method to track real-time substrate oxidation on a cell by cell basis in the isolated intact islet. This allows descrimination of pyruvate utilization in the beta and non beta cell islet populations. 30 mM pyruvate did not lead to art increased NAD(P)H in the beta-cell population of intact islets. Rather. a small population of islet cells usually located in the islet peril)l cry, displayed a rise in NA(P)H. This distribution is consistent with selective pyruvate oxidation by alpha-cells. Therefore pyruvate does not induce insulin secretion because it is not etficiently oxidized by pancreatic beta cells in the isolated intact islets.