Intracellular sodium ion activity and sodium transport in rabbit urinary bladder.

Abstract

Intracellular potentials and the intracellular activities of Na+ and K+ were examined using conventional and ion-selective micro-electrodes. In animals on a normal diet, the intracellular Na+ activity was 8.6 .+-. 2.9 mM (mean .+-. SD) with a mean short-circuit current of 2.8 .+-. 0.9 .mu.A/cm2. In animals on a low-Na+ diet, the intracellular Na+ activity was 18.5 .+-. 9.9 mM with a short-circuit current of 4.5 .+-. 1.3 .mu.A/cm2 (mean .+-. SD). There was a correlation between short-circuit current and intracellular Na+ activity which could be fitted by a saturating hyperbolic relationship. Treatment of the tissue with ouabain and amiloride produced an increase and a decrease, respectively, in the intracellular Na+ activity. Treatment with aldosterone produced a large increase in short-circuit current with a substantial increase in intracellular Na+ activity. Intracellular Na+ activity does not seem to affect apical membrane permeability directly.