Inward-directed current generated by the Na+,K+ pump in Na(+)- and K(+)-free medium.
In Na(+)- and K(+)-free solution, an inward-directed current can be detected in Xenopus oocytes, which is inhibited by cardiac glycosides and activated by ATP. Therefore, it is assumed to be generated by the Na+,K+ pump. At negative membrane potentials, the pump current increases with more negative potentials and with increasing [H+] in the external medium. This current is not observed when Mg2+ instead of Ba2+ is the only divalent cation present in the bath medium, and it does not depend on whether Na+ or K+ is present internally. At 5 to 10 mM Na+ externally, maximum pump-generated current is obtained while no current can be detected in presence of physiological [Na+]. It is suggested that in low-Na+ and K(+)-free medium the Na+,K+ pump molecule can either form a conductive pathway that is permeable to Ba2+ or protons or operate in its conventional transport mode accepting Ba2+ as a K+ congener. A reversed pump mode or an electrogenic uncoupled Na(+)-efflux mode is excluded.
Efthymiadis
A
A
Max-Planck-Institut für Biophysik, Frankfurt/Main, Germany.
Rettinger
J
J
Schwarz
W
W
D000818:Animals; D001464:Barium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D003470:Culture Media; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects; D008274:Magnesium / Q000378:metabolism; D008564:Membrane Potentials; D009865:Oocytes; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014101:Torpedo; D014982:Xenopus laevis
D003470:Culture Media; D001464:Barium; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D011188:Potassium