Modulation of K+ conductance by intracellular pH in pancreatic β‐cells

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Abstract
Measurements of the effects of NH3/NH4 + on glucose-induced electrical activity in β-cells from microdis-sected mouse islets of Langerhans and on intracellular pH in single collagenase-isolated islets pre-loaded with a fluorescent pH probe were performed and are reported here. Application of NH3/NH+ 4 (15 mM) in the presence of glucose (11 mM) promptly hyperpolarized the β-cell membrane, reduced input resistance by 60% and blocked electrical activity. These changes were paralleled by an increase in islet fluorescence indicative of a cytosolic pH increase. Removal of NH4Cl initially stumulated electical activity, which returned to resting level with a time constant of 51 s. Concomitant with the removal of NH4C1 there was a drop in pHi followed by a slow return to resting level with a time constant of 83 s. The results suggest that the [Ca2+]-dependent K+ channel in the β-cell membrane is activated by a rise in cytosolic pH.