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Am J Physiol Cell Physiol 277: C280-C287, 1999;
0363-6143/99 $5.00
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Vol. 277, Issue 2, C280-C287, August 1999

Ammonium transport by the colonic H+-K+-ATPase expressed in Xenopus oocytes

Marc Cougnon1, Patrice Bouyer1, Frédéric Jaisser2, Aleksander Edelman1, and Gabrielle Planelles1

1 Faculté de Médecine Necker, Institut National de la Santé et de la Recherche Médicale U. 467, Université Paris V, F-75015 Paris; and 2 Faculté de Médecine Xavier Bichat, Institut National de la Santé et de la Recherche Médicale U. 478, Université Paris VII, F-75018 Paris, France

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), NH4Cl induced a decrease in 86Rb uptake and the initial rate of intracellular acidification induced by extracellular NH4Cl 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 NH4Cl. 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 86Rb 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.

86Rb influx; intracellular sodium and pH measurements


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