Peritubular pH and transtubular potentials in isolated perfused cortical collecting ducts of rabbit kidney.

1. Cortical collecting ducts were dissected from slices of rabbit kidney, then perfused in vitro.2. Transtubular electrical potentials were measured before and after abrupt changes in peritubular fluid pH.3. Variation in peritubular fluid pH, induced either by alteration in HCO(3) (-) concentration or in H(2)PO(4) (-)/HPO(4) (2-) ratio, produced biphasic responses in potential. Thus, reduction in pH caused an immediate fall, and then a prolonged and marked rise, in transtubular potential. The converse occurred on raising the pH.4. Variation in luminal fluid pH between pH 4.85 and pH 7.35 did not alter this pattern of response.5. In contrast to the above, reduction of peritubular fluid pH by elevation of P(CO2) produced either no effect or a decrease in transtubular potential.6. The transtubular potential of the cortical collecting duct appears to be a function of the pH gradient across some as yet unidentified part of the wall of the duct.