Pancreatic islet B-cell individual variability rather than subpopulation heterogeneity

Abstract

Isolated rat pancreatic islet B-cells loaded with the Ca 2+-sensitive fluorochrome Fluo-3 were examined by single-step flow cytometry at increasing concentrations of d-glucose (1.0 to 20.0 mM). The near forward scatter of light was unaffected by changes in hexose concentration. The Fluo-3 fluorescent signal slightly decreased when the glucose concentration was raised from 1.0 to 5.0 mM, and progressively increased at higher hexose concentrations. The fluorescence attributable to endogenous NAD(P)H increased dramatically throughout the full range of d-glucose concentration, with a typical sigmoidal concentration-response relationship. No evidence for a bimodal frequency distribution of these variables was found, whether at low or high d-glucose concentrations. The 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 at high than at low d-glucose concentrations. These findings 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 argue against the existence of subpopulation heterogeneity in their responsiveness to d-glucose.