title: Effects of ammonia on bicarbonate transport in the cortical collecting duct.
abstract: Both acidosis and hypokalemia stimulate renal ammoniagenesis, and both regulate urinary proton and potassium excretion. We hypothesized that ammonia might play an important role in this processing by stimulating H(+)-K(+)-ATPase-mediated ion transport. Rabbit cortical collecting ducts (CCD) were studied using in vitro microperfusion, bicarbonate reabsorption was measured using microcalorimetry, and intracellular pH (pH(i)) was measured using the fluorescent, pH-sensitive dye, 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Ammonia caused a concentration-dependent increase in net bicarbonate reabsorption that was inhibited by luminal addition of either of the H(+)-K(+)-ATPase inhibitors, Sch-28080 or ouabain. The stimulation of net bicarbonate reabsorption was not mediated through apical H(+)-ATPase, basolateral Na(+)-K(+)-ATPase, or luminal electronegativity. Although ammonia caused intracellular acidification, similar changes in pH(i) induced by inhibiting basolateral Na(+)/H(+) exchange did not alter net bicarbonate reabsorption. We conclude that ammonia regulates CCD proton and potassium transport, at least in part, by stimulating apical H(+)-K(+)-ATPase.
authors.affiliation: Division of Nephrology, Gainesville Veterans Affairs Medical Center, Gainesville, Florida 32610-0224, USA.
authors.forename: A E
authors.initials: AE
authors.lastname: Frank
authors.forename: C S
authors.initials: CS
authors.lastname: Wingo
authors.forename: I D
authors.initials: ID
authors.lastname: Weiner
mesh_terms: D000641:Ammonia / Q000494:pharmacology*; D000818:Animals; D001639:Bicarbonates / Q000493:pharmacokinetics*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology*; D007685:Kidney Tubules, Collecting / Q000187:drug effects* / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D054328:Proton Pump Inhibitors; D011817:Rabbits
chemical_list: D001639:Bicarbonates; D004791:Enzyme Inhibitors; D007093:Imidazoles; D054328:Proton Pump Inhibitors; C035235:Sch 28080; D010042:Ouabain; D000641:Ammonia