title: Ammonium transport by the colonic H(+)-K(+)-ATPase expressed in Xenopus oocytes.
abstract: Functional expression of the rat colonic H(+)-K(+)-ATPase was obtained by coexpressing its catalytic alpha-subunit and the beta(1)-subunit of the Na(+)-K(+)-ATPase in Xenopus laevis oocytes. We observed that, in oocytes expressing the rat colonic H(+)-K(+)-ATPase but not in control oocytes (expressing beta(1) alone), NH(4)Cl induced a decrease in (86)Rb uptake and the initial rate of intracellular acidification induced by extracellular NH(4)Cl was enhanced, consistent with NH(+)(4) influx via the colonic H(+)-K(+)-ATPase. In the absence of extracellular K(+), only oocytes expressing the colonic H(+)-K(+)-ATPase were able to acidify an extracellular medium supplemented with NH(4)Cl. In the absence of extracellular K(+) and in the presence of extracellular NH(+)(4), intracellular Na(+) activity in oocytes expressing the colonic H(+)-K(+)-ATPase was lower than that in control oocytes. A kinetic analysis of (86)Rb uptake suggests that NH(+)(4) acts as a competitive inhibitor of the pump. Taken together, these results are consistent with NH(+)(4) competition for K(+) on the external site of the colonic H(+)-K(+)-ATPase and with NH(+)(4) transport mediated by this pump.
authors.affiliation: Faculté de Médecine Necker, Institut National de la Santé et de la Recherche Médicale U. 467, Université Paris V, F-75015 Paris, France.
authors.forename: M
authors.initials: M
authors.lastname: Cougnon
authors.forename: P
authors.initials: P
authors.lastname: Bouyer
authors.forename: F
authors.initials: F
authors.lastname: Jaisser
authors.forename: A
authors.initials: A
authors.lastname: Edelman
authors.forename: G
authors.initials: G
authors.lastname: Planelles
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D003106:Colon / Q000201:enzymology / Q000378:metabolism*; D005260:Female; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism*; D007477:Ions; D009865:Oocytes; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D051381:Rats; D012413:Rubidium / Q000493:pharmacokinetics; D014982:Xenopus laevis
chemical_list: D007477:Ions; D000644:Quaternary Ammonium Compounds; D017506:H(+)-K(+)-Exchanging ATPase; D012413:Rubidium