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Inward-directed current generated by the Na+,K+ pump in Na+- and K+-free medium

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Efthymiadis,  Athina
Department of Cell Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Rettinger,  Jürgen
Department of Cell Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Schwarz,  Wolfgang
Department of Cell Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Efthymiadis, A., Rettinger, J., & Schwarz, W. (1993). Inward-directed current generated by the Na+,K+ pump in Na+- and K+-free medium. Cell Biology International, 17(12), 1107-1116. doi:10.1006/cbir.1993.1043.


Cite as: https://hdl.handle.net/21.11116/0000-0008-3913-3
Abstract
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.