A conformation of Na(+)-K+ pump is permeable to proton.
The Na(+)-K+ pump is thought to operate through a two-conformation (E1-E2) transport cycle in which the cation binding sites are accessible only from one side at a time. Using Na(+)-loaded Xenopus oocytes in which Na(+)-K+ pumps were overexpressed by injection of cRNA of the Xenopus Na(+)-K+ pump alpha-and beta-sub units, we observed a Na(+)-K+ pump-mediated (ouabain-sensitive) inward current in the absence of other transportable cations, except H+, in the external solution. This inward current was strongly inwardly rectifying, pH dependent, and larger at acid pH. Under conditions favoring a large ouabain-sensitive inward current, we observed a ouabain-sensitive intracellular acidification, and the amplitude of the acidification was significantly related to the ouabain-sensitive current, indicating that this current was carried by protons. The reversal potential of the ouabain-sensitive current was dependent on external pH as expected for a proton-conductive pathway. We conclude that in the absence of external K+ the Na(+)-K+ pump can mediate a large inward electrogenic transport of proton. This is most easily explained by the hypothesis that the E2 conformation of the Na(+)-K+ pump with cation binding sites exposed to the outside is accessible to protons from both sides and thus provides a channellike pathway for protons.
Wang
X
X
Institute of Pharmacology and Toxicology, University of Lausanne, Switzerland.
Horisberger
J D
JD
D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D002412:Cations; D004553:Electric Conductivity; D005260:Female; D015870:Gene Expression; D006863:Hydrogen-Ion Concentration; D009865:Oocytes / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011487:Protein Conformation; D011522:Protons; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D014982:Xenopus laevis
D002412:Cations; D011522:Protons; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase