Ion transport in cortical collecting tubule; effect of amiloride.

STONER, L. C., M. B. BURG, AND J. ORLOFF. Ion transport in cortical collecting tubule; effect of amiloride. Am. J. Physiol. 227(2) : 453-459. 1974.-T b 1 u u es were dissected from rabbit kidneys and perfused in vitro. In cortical collecting tubules the transepithelial electrical potential difference (PD) was 35 mV (lumen negative). There was net active sodium reabsorption from the lumen and net active potassium secretion into the lumen. There was net chloride reabsorption that was probably passive, but the analysis of the mechanism of chloride transport was complicated by the presence of chloride exchange diffusion. Amiloride (10-j M) in the lumen inhibited sodium and potassium transport and caused a reversal of the polarity of the PD; 10B4 M amiloride in the bath had no effect. The positive PD was most likely caused by urinary acidification and decreased toward zero when acetazolamide was added to the bath, or when CO2 was eliminated from the bathing solutions. In the thick ascending limb of Henle’s loop the PD was +5.8 mV, which is attributed to active chloride reabsorption. Amiloride had no effect on either the PD or the net chloride transport. We conclude that amiloride inhibits active sodium and potassium transport in the cortical collecting tubule, but does not inhibit active chloride transport in the thick ascending limb, and that these effects account for the action of the drug previously observed in the intact kidney.