QUANTITATIVE SUBCELLULAR IMAGING OF GLUCOSE-METABOLISM WITHIN INTACT PANCREATIC-ISLETS

Studies of dispersed beta cells have been used to infer their behavior in the intact pancreatic islet. When dispersed, beta cells exhibit mu ltiple metabolic glucose-response populations with different insulin s ecretion properties, This has led to a model for glucose-dependent ins ulin secretion hom the islet based on a step-wise recruitment of indiv idual beta cells. However, previously reported synchronous and uniform Ca2+ activity and electrical responses indicate that beta cell behavi or within intact islets is more uniform. Therefore, uncertainty remain s whether beta cell metabolic heterogeneity is functionally important in intact islets. We have used two-photon excitation microscopy to mea sure and compare the glucose-induced NAD(P)H autofluorescence response in dispersed beta cells and within intact islets, Over 90% of beta ce lls in intact islets responded to glucose with significantly elevated NAD(P)H levels, compared with less than 70% of dispersed beta cells, I n addition, all responding beta cells within intact islets exhibited a sigmoidal glucose dose response behavior with inflection points of si milar to 8 mM glucose, These results suggest that beta cell heterogene ity may be functionally less important in the intact islet than has be en predicted hom studies of dispersed beta cells and support the role of glucokinase as the rate-limiting enzyme in the beta cell glucose re sponse.