Intracellular potassium in cells of the proximal tubule of Necturns maculosus.

Abstract

Using double-barreled K+ selective liquid ion-exchange microelectrodes intracellular K+ activity and the peritubular potential difference (PD) were measured simultaneously in single cells of Necturus proximal tubules. Proximal tubular fluid K+ activity and the transepithelial PD were also measured simultaneously. Kidney slices analyzed by flame photometry yielded a mean K+ concentration of 103.0±1.8 mM per Kg cell water. This electrometric study yielded a mean K+ activity of 58.7±2.3 mM, thus giving a low value of 0.57 for the mean ionic activity coefficient. The electrometric mean proximal tubule fluid K+ activity of 5.4±0.1 mM and plasma K+ activity of 2.8±0.3 mM yield a fluid/plasma activity ratio of 1.9±0.2. The calculated K+ equilibrium potentials (as calculated from the activity ratios) across the whole proximal tubular epithelium, its luminal cell boundary and its peritubular cell boundary are not significantly different from their respective measured membrane PDs. This signifies that K+ is in electro-chemical equilibrium distribution across the boundaries that separate the different compartments of the proximal tubular system.