Potassium reabsorption in the proximal tubule of the dog nephron.

Abstract

Proximal tubular fluid to plasma K and inulin ratios were determined in 4 different experimental conditions: hydropenia; hydropenia with renal arterial constriction; K loading with acetazolamide administration; and isotonic saline loading. The mean tubular fluid to plasma K concentration ratio was 1.16 in normal hydropenic dogs, 1.12 in hydropenic dogs with reduced glomerular filtration rate produced by renal arterial constriction, 1.00 in K-loaded dogs receiving acetazolamide, and 0.88 during saline loading. Fractional reabsorption of K in the proximal tubule was independent of filtration rate and not affected by either inhibition of proximal tubular Na reabsorption or inhibition of H ion secretion. Inhibition of proximal tubular H ion secretion in the K-loaded dog depressed Na reabsorption in this segment. The results further support the concept that K is extensively reabsorbed in the proximal tubule and that nephron segments more distal than the accessible portions of the proximal tubule are responsible for adjustments in the rate of K excretion..