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

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. Also intracellular K+ and N+ concentrations in the same gland were determined by chemical analyses for comparison with the intracellular K+ activity data. The activity coefficient for intracellular K+ thus obtained was 0.67, indicating that virtually all K+ ions in the cells are in diffusible and osmotically active form. Under control conditions, measured values of the resting membrane potential (Em), alpha Ki and K+ equilibrium potential (EK) were -40.2 +/- 0.6 mV (S.E., n = 163), -88.5 +/- 1.4 mM (S.E., n = 163), -83 mV respectively. Electrochemical potential differences for K+ across the basolateral membrane (delta micro K/F) were approximately +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). These results suggest that the membrane permeability increases to K+ upon stimulation. Possible changes in membrane permeabilities to Na+ and Cl- were also discussed.