Modulation of gating of a metabolically regulated, ATP-dependent K+ channel by intracellular pH in B cells of the pancreatic islet.

Membrane-permeant weak acids and bases, when applied to the bath, modulate the resting membrane potential and the glucose-induced electrical activity of pancreatic B cells, as well as their insulin secretion. These substances alter the activity of a metabolite-regulated, ATP-sensitive K+ channel which underlies the B-cell resting potential. We now present several lines of evidence indicating that the channel may be directly gated by pHi. (1) The time course of K+(ATP) channel activity during exposure to and washout of NH4Cl under a variety of experimental conditions, including alteration of the electrochemical gradient for NH4Cl entry and inhibition of the Na+o/H+i exchanger, resembles the time course of pHi measured in other cell types that have been similarly treated. (2) Increasing pHo over the range 6.25-7.9 increases K+(ATP) channel activity in cell-attached patches where the cell surface exposed to the bath has been permeabilized to H+ by the application of the K+/H+ exchanger nigericin. (3) Increasing pHi over a similar range produces similar effects on K+(ATP) channels in inside-out excised patches exposed to small concentrations of ATPi. The physiological role of delta pHi in the metabolic gating of this channel remains to be explored.