Electrochemical potentials of potassium in proximal renal tubule of rat

Summary 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.