Intracellular potassium activity (aKi) has been determined in absorptive cells lining the villi of isolated, stripped proximal segments of Amphiuma small intestine. With single-barreled liquid ion-exchanger microelectrodes aKi = 41.6 +/- 1.5 mM in normal chloride buffer; with double-barreled microelectrodes constructed by a new method aKi = 38.5 +/- 2.4 mM. Also, by the latter approach aKi = 41.1 +/- 2.1 mM in buffer in which potassium was elevated to 5 meq/liter and aKi = 44.2 +/- 1.3 mM in sulfate buffer with the same bath potassium concentration. Since the calculated potassium equilibrium potential exceeds the membrane potential this ion is accumulated by the intestinal absorptive cell. A major portion of cellular potassium is bound or compartmentalized since the intracellular potassium activity coefficient is very low. A layer exists near the villi in which the potassium activity exceeds that in the bath buffer solution.
- Copyright © 1976 by American Physiological Society