Plasma membrane electron transport in pancreatic beta-cells is mediated in part by NQO1

TitlePlasma membrane electron transport in pancreatic beta-cells is mediated in part by NQO1
Publication TypeJournal Article
Year of Publication2011
AuthorsGray J.P, Eisen T., Cline G.W, Smith P.J, Heart E.
JournalAm J Physiol Endocrinol MetabAm J Physiol Endocrinol Metab
Volume301
PaginationE113-21
Date PublishedJul
ISBN Number1522-1555 (Electronic)<br/>0193-1849 (Linking)
Accession Number21505151
KeywordsAdenosine Triphosphate/metabolism, Animals, Antioxidants/pharmacology, Cell Membrane/drug effects/*metabolism, Cells, Cultured, Dose-Response Relationship, Drug, Electron Transport/drug effects/genetics, Enzyme Inhibitors/pharmacology, Glucose/pharmacology, inhibitors/genetics/metabolism/*physiology, Insulin-Secreting Cells/drug effects/*metabolism, Insulin/secretion, Male, Mice, Mitochondria/drug effects/metabolism, Models, Biological, NAD(P)H Dehydrogenase (Quinone)/antagonists &, NAD/metabolism
Abstract

Plasma membrane electron transport (PMET), a cytosolic/plasma membrane analog of mitochondrial electron transport, is a ubiquitous system of cytosolic and plasma membrane oxidoreductases that oxidizes cytosolic NADH and NADPH and passes electrons to extracellular targets. While PMET has been shown to play an important role in a variety of cell types, no studies exist to evaluate its function in insulin-secreting cells. Here we demonstrate the presence of robust PMET activity in primary islets and clonal beta-cells, as assessed by the reduction of the plasma membrane-impermeable dyes WST-1 and ferricyanide. Because the degree of metabolic function of beta-cells (reflected by the level of insulin output) increases in a glucose-dependent manner between 4 and 10 mM glucose, PMET was evaluated under these conditions. PMET activity was present at 4 mM glucose and was further stimulated at 10 mM glucose. PMET activity at 10 mM glucose was inhibited by the application of the flavoprotein inhibitor diphenylene iodonium and various antioxidants. Overexpression of cytosolic NAD(P)H-quinone oxidoreductase (NQO1) increased PMET activity in the presence of 10 mM glucose while inhibition of NQO1 by its inhibitor dicoumarol abolished this activity. Mitochondrial inhibitors rotenone, antimycin A, and potassium cyanide elevated PMET activity. Regardless of glucose levels, PMET activity was greatly enhanced by the application of aminooxyacetate, an inhibitor of the malate-aspartate shuttle. We propose a model for the role of PMET as a regulator of glycolytic flux and an important component of the metabolic machinery in beta-cells.