NADH shuttle system regulates KATP channel-dependent pathway and steps distal to cytosolic Ca2+ concentration elevation in glucose-induced insulin secretion.

The NADH shuttle system is composed of the glycerol phosphate and malate-aspartate shuttles. We generated mice that lack mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH), a rate-limiting enzyme of the glycerol phosphate shuttle. Application of aminooxyacetate, an inhibitor of the malate-aspartate shuttle, to mGPDH-deficient islets demonstrated that the NADH shuttle system was essential for coupling glycolysis with activation of mitochondrial ATP generation to trigger glucose induced insulin secretion. The present study revealed that blocking the NADH shuttle system severely suppressed closure of the ATP-sensitive potassium (K-ATP) channel and depolarization of the plasma membrane in response to glucose in beta cells, although properties of the K-ATP channel on the excised beta cell membrane were unaffected. In mGPDH-deficient islets treated with aminooxyacetate, Ca2+ influx through the plasma membrane induced by a depolarizing concentration of KCl in the presence of the K-ATP channel opener diazoxide restored insulin secretion. However, the level of the secretion was only similar to 40% of wild-type controls. Thus, glucose metabolism through the NADH shuttle system leading to efficient ATP generation is pivotal to activation of both the K-ATP channel-dependent pathway and steps distal to an elevation of cytosolic Ca2+ concentration in glucose-induced insulin secretion.