title: Acetate transport in the S3 segment of the rabbit proximal tubule and its effect on intracellular pH.
abstract: We monitored intracellular pH (pHi) in isolated perfused S3 segments of the rabbit proximal tubule, and studied the effect of acetate (Ac-) transport on pHi. pHi was calculated from the absorbance spectrum of 4',5'-dimethyl-5-(and 6) carboxyfluorescein trapped intracellularly. All solutions were nominally HCO3(-)-free. Removal of 10 mM Ac- from bath and lumen caused pHi to rapidly rise by approximately 0.2, and then to decline more slowly to a value approximately 0.35 below the initial one. Removal of only luminal Ac- caused pHi changes very similar to those resulting from bilateral removal of Ac-. When Ac- was removed from bath only, pHi rose rapidly at first, and then continued to rise more slowly. Readdition of Ac- to bath caused pHi to rapidly fall to a value slightly higher than the one prevailing before the removal of Ac- from the bath. In experiments in which Ac- was first removed from both bath and lumen, readdition of 10 mM Ac- to only lumen caused a rapid but small acidification, followed by a slower alkalinization that brought the pHi near the value that prevailed before the bilateral removal of Ac-. The alkalinizing effects caused by the readdition of 10 or 0.5 mM Ac- were indistinguishable. When Ac- was returned to only lumen in the absence of luminal Na+, there was a small and rapid pHi decrease, but no pHi recovery. Removal of Na+ from bath did not affect the pHi transients caused by the addition of Ac- to lumen. In experiments in which Ac- was first removed bilaterally, readdition of Ac- to only bath caused a large and sustained drop in pHi, whereas the subsequent removal of Ac- from the bath caused a slight alkalinization. These pHi changes caused by readdition or removal of Ac- from baths were unaffected by the absence of external Na+. We conclude that there is a Na+/Ac- cotransporter at the luminal membrane, and pathways for acetic acid transport at both luminal and basolateral membranes. The net effect of Ac- transport on pHi is to alkalinize the cell as a result of the luminal entry of Na+/Ac-, which is followed by the luminal and basolateral exit of acetic acid.
authors.affiliation: Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
authors.forename: N L
authors.initials: NL
authors.lastname: Nakhoul
authors.forename: W F
authors.initials: WF
authors.lastname: Boron
mesh_terms: D000085:Acetates / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D007700:Kinetics; D010477:Perfusion; D010710:Phosphates / Q000378:metabolism / Q000494:pharmacology; D011817:Rabbits; D012964:Sodium / Q000378:metabolism
chemical_list: D000085:Acetates; D010710:Phosphates; D012964:Sodium