Effect of potassium adaptation on the distribution of potassium, sodium and chloride across the apical membrane of renal tubular cells.
To assess the effect of K adaptation on the electrolyte concentrations of renal tubular cells and on the concentration gradients across the luminal membrane, electron microprobe analysis was employed on freeze-dried cryosections of the renal cortex and on freeze-dried samples of tubular fluid in control and high-K rats. The measurements were performed in individual cells of the proximal and superficial distal tubule and on samples of tubular fluid obtained by free flow micropuncture from proximal and early and late distal collection sites. The ingestion of a potassium-rich diet for at least 10 days together with an acute potassium load of 0.4 mmol/kg/h led to a small increase in potassium concentration of about 7 mmol/kg wet weight (w.w.) in all cell types analysed. In distal convoluted tubule, connecting tubule and principal cells sodium concentration was markedly decreased by 4, 4, and 6 mmol/kg w.w., respectively, while no significant changes in sodium concentration were found in proximal tubule and intercalated cells. No consistent changes in cell chloride could be observed under K adaptation. Analysis of the tubular fluid samples showed that the K concentration gradient across the apical cell membrane of all distal tubular cell types investigated was diminished in the high-K rats. The concentration gradient for sodium entry, however, was clearly enhanced in the distal convoluted tubule, connecting tubule and principal cells.(ABSTRACT TRUNCATED AT 250 WORDS)