Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
J Membr Biol
2004 Mar 15;1982:65-76. doi: 10.1007/s00232-004-0660-4.
Show Gene links
Show Anatomy links
Effect of extracellular pH on presteady-state and steady-state current mediated by the Na+/K+ pump.
Vasilyev A
,
Khater K
,
Rakowski RF
.
???displayArticle.abstract???
A ouabain sensitive inward current occurs in Xenopus oocytes in Na+ and K(+)-free solutions. Several laboratories have investigated the properties of this current and suggested that acidic extracellular pH (pHo) produces a conducting pathway through the Na+/K+ pump that is permeable to H+ and blocked by [Na+]o. An alternative suggestion is that the current is mediated by an electrogenic H(+)-ATPase. Here we investigate the effect of pHo and [Na+]o on both transient and steady-state ouabain-sensitive current. At alkaline or neutral pHo the relaxation rate of pre-steady-state current is an exponential function of voltage. Its U-shaped voltage dependence becomes apparent at acidic pHo, as predicted by a model in which protonation of the Na+/K+ pump reduces the energy barrier between the internal solution and the Na+ occluded state. The model also predicts that acidic pHo increases steady-state current leak through the pump. The apparent pK of the titratable group(s) is approximately 6, suggesting that histidine is involved in induction of the conductance pathway. 22Na efflux experiments in squid giant axon and current measurements in oocytes at acidic pHo suggest that both Na+ and H+ are permeant. The acid-induced inward current is reduced by high [Na+]o, consistent with block by Na+. A least squares analysis predicts that H+ is four orders of magnitude more permeant than Na+, and that block occurs when 3 Na+ ions occupy a low affinity binding site (K(0.5) = 130 +/- 30 m M) with a dielectric coefficient of 0.23 +/- 0.03. These data support the conclusion that the ouabain-sensitive conducting pathway is a result of passive leak of both Na+ and H+ through the Na+/K+ pump.
Brinley,
Sodium extrusion by internally dialyzed squid axons.
1967, Pubmed
Brinley,
Sodium extrusion by internally dialyzed squid axons.
1967,
Pubmed
Cornelius,
Uncoupled Na+-efflux on reconstituted shark Na,K-ATPase is electrogenic.
1989,
Pubmed
Cornelius,
Variable stoichiometry in reconstituted shark Na,K-ATPase engaged in uncoupled efflux.
1990,
Pubmed
De Weer,
Voltage dependence of the apparent affinity for external Na(+) of the backward-running sodium pump.
2001,
Pubmed
Efthymiadis,
Inward-directed current generated by the Na+,K+ pump in Na(+)- and K(+)-free medium.
1993,
Pubmed
,
Xenbase
Gadsby,
Steady-state current-voltage relationship of the Na/K pump in guinea pig ventricular myocytes.
1989,
Pubmed
Gadsby,
Charge movements via the cardiac Na,K-ATPase.
1992,
Pubmed
Gadsby,
Extracellular access to the Na,K pump: pathway similar to ion channel.
1993,
Pubmed
Garrahan,
The behaviour of the sodium pump in red cells in the absence of external potassium.
1967,
Pubmed
Glynn,
ATP hydrolysis associated with an uncoupled sodium flux through the sodium pump: evidence for allosteric effects of intracellular ATP and extracellular sodium.
1976,
Pubmed
Holmgren,
Pre-steady-state transient currents mediated by the Na/K pump in internally perfused Xenopus oocytes.
1994,
Pubmed
,
Xenbase
Polvani,
Protons as substitutes for sodium and potassium in the sodium pump reaction.
1988,
Pubmed
Rakowski,
Simultaneous measurement of changes in current and tracer flux in voltage-clamped squid giant axon.
1989,
Pubmed
Rakowski,
Stoichiometry and voltage dependence of the sodium pump in voltage-clamped, internally dialyzed squid giant axon.
1989,
Pubmed
Rakowski,
A negative slope in the current-voltage relationship of the Na+/K+ pump in Xenopus oocytes produced by reduction of external [K+].
1991,
Pubmed
,
Xenbase
Rakowski,
Charge movement by the Na/K pump in Xenopus oocytes.
1993,
Pubmed
,
Xenbase
Rettinger,
Characteristics of Na+/K(+)-ATPase mediated proton current in Na(+)- and K(+)-free extracellular solutions. Indications for kinetic similarities between H+/K(+)-ATPase and Na+/K(+)-ATPase.
1996,
Pubmed
,
Xenbase
Sagar,
Access channel model for the voltage dependence of the forward-running Na+/K+ pump.
1994,
Pubmed
,
Xenbase
Taglialatela,
Novel voltage clamp to record small, fast currents from ion channels expressed in Xenopus oocytes.
1992,
Pubmed
,
Xenbase
Wang,
A conformation of Na(+)-K+ pump is permeable to proton.
1995,
Pubmed
,
Xenbase
Wuddel,
Electrogenicity of the sodium transport pathway in the Na,K-ATPase probed by charge-pulse experiments.
1995,
Pubmed