Amiloride-sensitive regulation of intracellular pH in B-cells: Activation by glucose

Abstract

Alterations in intracellular pH (pH i) generated by metabolism of glucose has been proposed to be a transduction device for controlling changes in K + conductance in the plasma membrane of the B-cell leading to depolarization and cyclic variations in the membrane potential associated with spike activity. The influence of permeable weak acids or bases and amiloride inhibition of H + extrusion by a Na:H exchanger on glucose-induced electrical activity has suggested that the electrical events are pH-sensitive. In order to document that these conditions alter pH i, we determined the influence of glucose, propionic acid, and NH 4Cl, in the presence or absence of amiloride on pH i of rat islets using [ 14C] DMO. Glucose, 2.8 mmol/L decreased pH i by .09 unit compared to the absence of glucose (pH i = 7.08 ± .01, M ± SEM) and 16.7 mmol/L glucose reduced pH i by .19 unit. The glucose dose-related decrease in pH i yielded a half-maximal response at 4 mmol/L. The addition of 0.1 mmol/L amiloride had no influence on pH i without glucose and decreased pH i in the presence of 2.8 mmol/L glucose by .14 unit. The addition of 20 mmol/L propionic acid to 2.8 mmol/L glucose reduced pH i to 6.85 ± .05, whereas 20 mmol/L NH 4Cl increased pH i to 7.27 ± .07. The addition of amiloride did not further lower the reduction in pH i elicited by 20 mmol/L propionic acid or 16.7 mmol/L glucose. These results suggest that the amiloride-sensitive Na:H exchanger plays a major role in regulation of pH i, but another modality for pH i regulation exists to compensate for inhibition of Na:H exchange under conditions of an acid load.