title: Pathways for HCO3-reabsorption in mouse medullary collecting duct segments.
abstract: To determine pathways of HCO3- reabsorption in the collecting duct of the mouse kidney, the outer medullary collecting duct (OMCD) and the terminal inner medullary collecting duct (IMCDt) were dissected and perfused at 1 to 2 nL/min, and total CO2 was measured by microfluorometry. In the OMCD, net HCO3- flux (JtCO2) was 12.2 +/- 0.7 pmol/min/mm tubule length and decreased to 6.9 +/- 0.6 pmol/min/mm tubule length (n = 5) with 10 mol/L Schering 28080 (SCH) in perfusate (P < .001) and to 7.7 +/- 0.6 pmol/min/mm tubule length (P < .004; n = 4) with 50 micromol/L diethylstilbestrol (DES), an inhibitor of H+-adenosine triphosphatase; together they reduced JtCO2 to 3.7 +/- 0.2 pmol/min/mm tubule length (P = .0002; n = 4). In IMCDt, JtCO2 was 10.9 +/- 1.1 pmol/min/mm tubule length, and it decreased to 4.3 +/- 0.9 pmol/min/mm tubule length (n = 4) with 10 micromol/L SCH in perfusate (P < .05) and to 7.0 +/- 1.1 pmol/min/mm tubule length (P < .05; n = 4) with 50 micromol/L DES; together they decreased JtCO2 to 2.3 +/- 0.3 pmol/min/mm tubule length (P < .002; n = 4). Ouabain (1 mmol/L), an inhibitor of colonic H-K-adenosine triphosphatase (cHKA), in perfusate had no effect on JtCO2 in either segment. Northern hybridization studies showed a high level of expression of gastric HKA (gHKA) in outer medulla and a low level in inner medulla; cHKA expression was undetectable. Thus, in normal mouse OMCD and IMCDt, HCO3- reabsorption is predominantly mediated by gHKA and H+-adenosine triphosphatase and not cHKA. A third isoform of HKA could be present in mouse IMCDt.
authors.affiliation: Department of Medicine, University of Cincinnati College of Medicine, and the Veterans Affairs Medical Center, Ohio, USA.
authors.forename: S
authors.initials: S
authors.lastname: Nakamura
authors.forename: H
authors.initials: H
authors.lastname: Amlal
authors.forename: M
authors.initials: M
authors.lastname: Soleimani
authors.forename: J H
authors.initials: JH
authors.lastname: Galla
mesh_terms: D000042:Absorption; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D003106:Colon / Q000201:enzymology; D004054:Diethylstilbestrol / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005753:Gastric Mucosa / Q000201:enzymology; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D007672:Kidney Cortex / Q000201:enzymology; D007679:Kidney Medulla / Q000201:enzymology / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008297:Male; D051379:Mice; D011188:Potassium / Q000494:pharmacology; D054328:Proton Pump Inhibitors; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D054328:Proton Pump Inhibitors; D004054:Diethylstilbestrol; D017506:H(+)-K(+)-Exchanging ATPase; D006180:Proton-Translocating ATPases; D011188:Potassium