THE MECHANISM OF POTASSIUM REABSORPTION IN THE PROXIMAL TUBULE OF THE RAT*

Open Access
Publisher Website
Google Scholar
Abstract
Simultaneous measurements of transtubular potential difference, ET, and of potassium concentration in tubular fluid and plasma, [K]tf and [K]p, have been obtained from proximal tubules of non-diuretic rats. All puncture sites were localized by microdissection. ET ranged from -8 to-49 mV. There was no correlation between magnitude of potential and location along the proximal tubule. In all segments of the proximal tubule, [K]tf tended to fall below [K]p. The mean potassium concentration ratio, [K]tf/[K]p, of 0.92 + 0.13 (standard deviation) was significantly less than unity. Since it may be presumed that extensive water reabsorption occurs in the proximal convolution during antidiuresis, these data indicate extensive net potassium reabsorption. In addition, [K]xf was invariably lower than that predicted for the corresponding ET by the Nernst equation, demonstrating that the reabsorption of potassium must occur against an electrochemical gradient. It is concluded from an analysis of the electrochemical potentials of potassium in tubular fluid, cell water, and extracellular fluid that an active transport mechanism for potassium exists at the luminal cell membrane.