Intracellular potassium ion activity in resting and stimulated mouse pancreas and submandibular gland

Intracellular potassium ion activities (aⁱ_K⁺) and membrane potentials were measured with double-barrelled, potassium-specific microelectrodes in superfused mouse pancreas and submandibular gland. Stimulation with the cholinergic agonist bethanechol caused a marked decrease in aⁱ_K⁺ in the submandibular gland, whereas no change in aⁱ_K⁺ could be detected in the pancreas. This indicates that bethanechol increases the permeability of the cell membranes to potassium ions in the submandibular gland but not in the pancreas. Pancreatic acinar cells hyperpolarized promptly when the extracellular potassium ion activity was restored after a prolonged period of potassium deprivation. In comparison, the recovery of aⁱ_K⁺ was a slow process. This finding gives support to the view that the hyperpolarization is due to electrogenic sodium pumping.