Electrochemical potentials of potassium in proximal renal tubule of rat.

Abstract

By means of double-barreled K+ selective liquid ion-exchange microelectrodes, the electrical potential differences across individual cell membranes were determined simultaneously with the K+ concentration in single cellular elements of the proximal tubular epithelium of the rat. Proximal tubular fluid [K+] and plasma [K+] were also determined electrometrically. Thin cortical slices of the rat kidney analyzed by flame photometry yielded a mean [K+] of 136.3±4.2 mM per kg cell water. This electrometric study yielded a mean intracellular [K+] of 54.4±2.5 mM, a value which is about 1/3 of the total K+ content of proximal tubule cells. The electrometric mean proximal tubule fluid (second half) [K+] was 3.7±0.1 mM while plasma [K+] was 4.3±0.1 mM, yielding a fluid/plasma concentration ratio of 0.85±0.02. The calculated K+ equilibrium potentials (E K )across the two individual from their respective measured membrane electrical PDs. This signifies that K+ exhibits an electrochemical equilibrium distribution across the luminal and peritubular cell boundaries of the proximal tubular epithelium. Thus it is no longer necessary to postulate the presence of an active K+ pump in either the luminal or peritubular cell membranes.