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Journal Article

Characteristics of the Na+/K+-ATPase from Torpedo californica expressed in Xenopus oocytes: a combination of tracer flux measurements with electrophysiological measurements

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

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Gu,  Quanbao
Department of Cell Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Schwarz, W., & Gu, Q. (1988). Characteristics of the Na+/K+-ATPase from Torpedo californica expressed in Xenopus oocytes: a combination of tracer flux measurements with electrophysiological measurements. Biochimica et Biophysica Acta-Biomembranes, 945(2), 167-174. doi:10.1016/0005-2736(88)90479-8.


Cite as: https://hdl.handle.net/21.11116/0000-0008-3F1B-5
Abstract
The Na+/K+-ATPase from electroplax of Torpedo californica was incorporated into the plasma membrane of Xenopus oocytes by microinjection of mRNA coding for the α- and β-subunit of the enzyme; the mRNAs were obtained by in vitro translation of cloned cDNAs (Noguchi et al. (1988) FEBS Lett. 225, 27–32). (1) Measurements of ouabain-sensitive membrane current revealed that the Na+/K+-ATPase of Torpedo is less sensitive to ouabain than the endogenous enzyme. (2) The ouabain-sensitive membrane currents in mRNA-injected oocytes exhibit similar voltage dependence as the currents generated by the endogenous ATPase of Xenopus oocytes; in particular, the current-voltage relation exhibits a maximum and a negative slope at potentials more positive than + 20 mV. (3) A maximum can also be detected if the rate of 22Na+ efflux is determined under different voltage-clamp conditions. If membrane current and rate of Na2+ efflux are determined simultaneously, a voltage-independent ratio between current and flux is obtained suggesting voltage-independent Na+-K+ stoichiometry. The data are compatible with a 3Na+–2K+ stoichiometry.