title: Expression of Na(+)-H+ exchange and ATP-dependent proton extrusion in growing rat IMCD cells.
abstract: As the last step of urinary acidification, the inner medullary collecting duct (IMCD) is thought to secrete protons into the tubular lumens by means of a H(+)-translocating adenosinetriphosphatase (H(+)-ATPase). However, recent studies have also shown the existence of Na(+)-H+ exchange activity in IMCD cells. Although the physiological function of the antiporter in IMCD cells is unknown, activation of Na(+)-H+ exchange in other cell-culture systems has been suggested to be closely associated with the process of cell growth. Thus presence of Na(+)-H+ exchange may relate to the growth phase of these cells. To examine intracellular pH (pHi) regulation in growing IMCD cells, we studied proton transport by Na(+)-dependent and Na(+)-independent mechanisms by microfluorimetry using the pHi-sensitive dye 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein acetoxymethyl ester (BCECF/AM). Actively growing cells, defined by [3H]thymidine incorporations, demonstrated an amiloride-sensitive Na(+)-dependent pHi recovery after an acid load. No pHi recovery was evident in the absence of Na+, indicating the importance of Na(+)-H+ exchange for pHi recovery. However, when evaluated in quiescent cells, Na(+)-dependent pHi recovery appeared to be diminished. Instead, a Na(+)-independent pHi recovery which was inhibitable by ATP depletion and by 1 mM N-ethylmaleimide was present, suggesting function of a H(+)-ATPase. These findings indicate that Na(+)-dependent proton extrusion activity (Na(+)-H+ exchange) but not Na(+)-independent proton extrusion activity is expressed during the rapid growth phase of IMCD cells, whereas the more quiescent cells express Na(+)-independent ATP-dependent proton extrusion activity and a possibly less active Na(+)-H+ exchanger.
authors.affiliation: Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: R C
authors.initials: RC
authors.lastname: Stanton
authors.forename: D C
authors.initials: DC
authors.lastname: Boxer
authors.forename: J L
authors.initials: JL
authors.lastname: Seifter
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000584:Amiloride / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D004261:DNA Replication; D005033:Ethylmaleimide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007679:Kidney Medulla / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D006180:Proton-Translocating ATPases / Q000378:metabolism; D011522:Protons; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers; D013936:Thymidine / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D000643:Ammonium Chloride; D000584:Amiloride; D000255:Adenosine Triphosphate; D012964:Sodium; D006180:Proton-Translocating ATPases; D005033:Ethylmaleimide; D013936:Thymidine