The relationship between distal tubular proton secretion and dietary potassium depletion: evidence for up-regulation of H+-ATPase

Background. Dietary potassium depletion is associated with elevated plasma bicarbonate concentration and enhanced bicarbonate reabsorption in the dist al tubule. The relationship between distal proton secretion and potassium s tatus was investigated by in vivo micro-perfusion of the superficial distal tubule. Methods, Experiments were performed on anaesthetized rats that had been mai ntained on either a low-potassium or control diet for 3-5 weeks prior to ex perimentation. The distal tubules were perfused at 10 nl/min with either a standard or a barium chloride-containing solution, and the late distal tubu lar transepithelial potential difference (V-te) and pH of the luminal fluid were recorded using a double-barrelled voltage and ion-sensitive microelec trode. Results. In control rats, the V-te was -40.7 +/- 2.4 mV and the tubular flu id pH was 6.44 +/- 0.07;in potassium-depleted animals, the V-te was -15.0 /- 1.4 mV and the pH was 6.76 +/- 0.03. The pH values in both groups of ani mals were significantly lower than would be predicted from the V-te and sys temic pH for passive H+ distribution, indicating active proton secretion. M oreover, in hypokalaemic rats, this difference from predicted pH was signif icantly greater than in control animals (control = 0.27 +/- 0.06 vs low-pot assium = 0.46 +/- 0.03; P < 0.01), suggesting enhanced active proton secret ion. During perfusion with a solution containing BaCl2, the late distal tub ule V-te became lumen positive in potassium-depleted rats, contrasting with an increased lumen negativity in potassium-replete controls. The barium-in duced lumen-positive potential difference observed in the hypokalaemic rats was abolished by intravenous administration of acetazolamide. Conclusion. These data are consistent with enhanced electrogenic proton sec retion (H+-ATPase) during dietary potassium deprivation.