Intracellular K+ activity in canine submandibular gland cells in resting and its change during stimulation.

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Abstract
Intracellular K+ activity (.alpha.Ki) and transmembrane potential differences were simultaneously measured with double-barreled K+ selective microelectrodes in superfused canine submandibular glands at rest and during stimulation. Intracellular K+ and Na+ concentrations in the same gland were determined by chemical analyses for comparison with the aKi data. The activity coefficient for intracellular K+ was 0.67, indicating that virtually all K+ in the cells are in diffusible and osmotically active form. Under control conditions, measured values of the resting membrane potential (Em), aKi and K+ equilibrium potential (EK) were -40.2 .+-. 0.6 mV (SE, n = 163), -88.5 .+-. 1.4 mM (SE, n = 163), -83 mV, respectively. Electrochemical potential differences for K+ across the basolateral membrane (.DELTA.~.mu.KF) were .apprx. +43 mV. Acetylcholine (ACh) induced an abrupt membrane hyperpolarization followed by a temporary fall of .alpha.Ki. The maximum rate of .alpha.Ki change in the cytoplasm during stimulated conditions was -35.5 .+-. 0.9 mM/min on the average (n = 10). Apparently, the membrane permeability increases to K+ upon stimulation. Possible changes in membrane permeabilities to Na+ and Cl- were also discussed.

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