Characteristics of the Na+/K+-ATPase from Torpedo californica expressed in Xenopus oocytes: a combination of tracer flux measurements with electrophysiological measurements.
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 alpha- and beta-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 Na+2 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.
Schwarz
W
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Max-Planck-Institut für Biophysik, Frankfurt am Main, F.R.G.
Gu
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QB
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000502:physiology; D004553:Electric Conductivity; D004557:Electric Organ / Q000201:enzymology; D008564:Membrane Potentials; D008845:Microinjections; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012333:RNA, Messenger / Q000008:administration & dosage; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D014101:Torpedo / Q000502:physiology*; D014982:Xenopus laevis
D012333:RNA, Messenger; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium