Nutrient-induced changes in the pH of pancreatic islet cells

Fluorescein rapidly accumulates in rat pancreatic islets exposed to fluorescein diacetate. The influence of environmental agents upon cellular pH was examined in fluorescein-labelled islets by recording their fluorescence intensity at 520 nm after excitation at 490 and 435 nm, respectively. Glucose caused a rapid, sustained and dose-related increase in cellular pH. Another nutrient secretagogue, 2-ketoisocaproic acid, also increased cellular pH. The stimulation of islet cells by non-nutrient secretagogues, e.g. by glibenclamide or in response to an increase in extracellular K+ concentration, decreased cellular pH, indicating that the nutrient-induced increase in cellular pH is not merely a consequence of stimulated Ca2+ inflow and/or insulin release. In either the presence of amiloride or absence of bicarbonate, glucose decreased cellular pH. These results strongly suggest that the acidification of islet cells which can be expected from the increased metabolism of glucose in glucose-stimulated islets is normally masked and overcome by stimulation of such processes as Na+/H+ and HCO3-/Cl- exchange.