Acidification of luminal fluid by the rabbit cortical collecting tubule perfused in vitro.

Abstract

The ability of the rabbit cortical collecting tubule to acidify the luminal fluid was determined with double-barreled antimony pH electrodes. In Na+/K+ Ringer the tubules maintained a transepithelial voltage (VToc) of -45.4 +/- 5.5 mV (bath grounded) and a minimum luminal fluid pH of 5.93 +/- 0.11. Chronic mineralocorticoid pretreatment of the rabbits caused the VToc to become more negative (-78.7 +/- 8.2 mV) and decreased the minimum luminal fluid pH to 5.43 +/- 0.16. In most tubules (control and mineralocorticoid-pretreated) the measured pH was more acidic than could be accounted for by either the lumen-negative VToc or CO2 equilibration of the perfusion fluid. When tubules were perfused and bathed in 0 Na+/0 K+ Ringer they developed a lumen-positive VToc, which was stimulated by mineralocorticoid, was sensitive to the PCO2 of the bathing solutions, but was not dependent on Cl- in either the luminal or bath solutions. Luminal acidification in the absence of Na+ and K+ (pH = 6.05 +/- 0.12) occurred against a lumen-positive VToc of +11.5 +/- 1.9 mV. Addition of 10(-4) M ouabain to the bath of tubules studied in Na+/K+ Ringer caused the VToc to reverse polarity and the luminal fluid pH to increase. In contrast, ouabain had no effect on either the lumen-positive VToc or the minimum luminal fluid pH when added to the bath of tubules in 0 Na+/0 K+ Ringer. Bath addition of 10(-4) M acetazolamide and/or 5 X 10(-4) M 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) caused alkalinization of the luminal fluid in tubules studied in either Na+/K+ or 0 Na+/0 K+ Ringer. In 0 Na+/0 K+ Ringer, acetazolamide and SITS reduced the lumen-positive VToc to near zero. The data support the existence of a distinct acidification mechanism in the rabbit cortical collecting tubule, which is both active and electrogenic.