Abstract
Intracellular K+ activity (aKi) 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 Na+ 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), aKi and K+ equilibrium potential (EK) were -40.2±0.6mV (S.E., n=163), -88.5±1.4mM (S.E., n=163), -83mV respectively. Electrochemical potential differences for K+ across the basolateral membrane (ΔμK/F) were approximately +43mV. Acetylcholine (ACh) induced an abrupt membrane hyperpolarization followed by a temporary fall of aKi. The maximum rate of aKi change in the cytoplasm during stimulated conditions was -35.5±0.9mM/min on the average (n=10). These results suggest that the membrane permeability increases to K+ upon stimulation. Possible changes in membrane permeabilities to (NaEK) and Cl- were also discussed.
