NADH shuttle system regulates K-ATP 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-as partate shuttles. We generated mice that lack mitochondrial glycerol-3-phos phate dehydrogenase (mGPDH), a rate-limiting enzyme of the glycerol phospha te shuttle. Application of aminooxyacetate, an inhibitor of the malate-aspa rtate shuttle, to mGPDH-deficient islets demonstrated that the NADH shuttle system was essential for coupling glycolysis with activation of mitochondr ial ATP generation to trigger glucose induced insulin secretion. The present study revealed that blocking the NADH shuttle system severely s uppressed closure of the ATP-sensitive potassium (K-ATP) channel and depola rization of the plasma membrane in response to glucose in beta cells, altho ugh properties of the K-ATP channel on the excised beta cell membrane were unaffected. In mGPDH-deficient islets treated with aminooxyacetate, Ca2+ in flux 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 syste m leading to efficient ATP generation is pivotal to activation of both the K-ATP channel-dependent pathway and steps distal to an elevation of cytosol ic Ca2+ concentration in glucose-induced insulin secretion.