PANCREATIC-ISLET B-CELL INDIVIDUAL VARIABILITY RATHER THAN SUBPOPULATION HETEROGENEITY

Isolated rat pancreatic islet B-cells loaded with the Ca2+-sensitive f luorochrome Fluo-3 were examined by single-step flow cytometry at incr easing concentrations of D-glucose (1.0 to 20.0 mM). The near forward scatter of light was unaffected by changes in hexose concentration. Th e Fluo-3 fluorescent signal slightly decreased when the glucose concen tration was raised from 1.0 to 5.0 mM, and progressively increased at higher hexose concentrations. The fluorescence attributable to endogen ous NAD(P)H increased dramatically throughout the full range of D-gluc ose concentration, with a typical sigmoidal concentration-response rel ationship. No evidence for a bimodal frequency distribution of these v ariables was found, whether at low or high D-glucose concentrations. T he dispersion of individual NAD(P)H measurements, as judged by either their coefficient of variation or the height of their modal peak, was less pronounced al high than al low D-glucose concentrations. These fi ndings document vastly different concentration-response relationships for metabolic and ionic variables in glucose-stimulated B-cells. They confirm that all B-cells do not display an identical behavior, but arg ue against the existence of subpopulation heterogeneity in their respo nsiveness to D-glucose.