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rdf:type |
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lifeskim:mentions |
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pubmed:issue |
5
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pubmed:dateCreated |
1994-8-12
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pubmed:abstractText |
The voltage dependence of steady state current produced by the forward mode of operation of the endogenous electrogenic Na+/K+ pump in Na(+)-loaded Xenopus oocytes has been examined using a two-microelectrode voltage clamp technique. Four experimental cases (in a total of 18 different experimental conditions) were explored: variation of external [Na+] ([Na]o) at saturating (10 mM) external [K+] ([K]o), and activation of pump current by various [K]o at 0, 15, and 120 mM [Na]o (tetramethylammonium replacement). Ionic current through K+ channels was blocked by Ba2+ (5 mM) and tetraethylammonium (20 mM), thereby allowing pump-mediated current to be measured by addition or removal of external K+. Control measurements and corrections were made for pump current run-down and holding current drift. Additional controls were done to estimate the magnitude of the inwardly directed pump-mediated current that was present in K(+)-free solution and the residual K(+)-channel current. A pseudo two-state access channel model is described in the Appendix in which only the pseudo first-order rate coefficients for binding of external Na+ and K+ are assumed to be voltage dependent and all transitions between states in the Na+/K+ pump cycle are assumed to be voltage independent. Any three-state or higher order model with only two oppositely directed voltage-dependent rate coefficients can be reduced to an equivalent pseudo two-state model. The steady state current-voltage (I-V) equations derived from the model for each case were simultaneously fit to the I-V data for all four experimental cases and yielded least-squares estimates of the model parameters. The apparent fractional depth of the external access channel for Na+ is 0.486 +/- 0.010; for K+ it is 0.256 +/- 0.009. The Hill coefficient for Na+ is 2.18 +/- 0.06, and the Hill coefficient for K+ (which is dependent on [Na]o) ranges from 0.581 +/- 0.019 to 1.35 +/- 0.034 for 0 and 120 mM [Na]o, respectively. The model provides a reasonable fit to the data and supports the hypothesis that under conditions of saturating internal [Na+], the principal voltage dependence of the Na+/K+ pump cycle is a consequence of the existence of an external high-field access channel in the pump molecule through which Na+ and K+ ions must pass in order to reach their binding sites.
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pubmed:grant |
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pubmed:commentsCorrections |
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-1333148,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-1646889,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-1652644,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-1653228,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-1880791,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2427727,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2430183,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2440883,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2443675,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2443682,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2544655,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2552127,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2582111,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2607334,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2850533,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2854181,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-2995541,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-3016280,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-3225842,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-5812424,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-6051803,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-6320453,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-7310856,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-7682009,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-8229858,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-8382257,
http://linkedlifedata.com/resource/pubmed/commentcorrection/8035166-8383596
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pubmed:language |
eng
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pubmed:journal |
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pubmed:citationSubset |
IM
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pubmed:chemical |
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pubmed:status |
MEDLINE
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pubmed:month |
May
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pubmed:issn |
0022-1295
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pubmed:author |
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pubmed:issnType |
Print
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pubmed:volume |
103
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pubmed:owner |
NLM
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pubmed:authorsComplete |
Y
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pubmed:pagination |
869-93
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pubmed:dateRevised |
2009-11-18
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pubmed:meshHeading |
pubmed-meshheading:8035166-Animals,
pubmed-meshheading:8035166-Cell Membrane,
pubmed-meshheading:8035166-Female,
pubmed-meshheading:8035166-Fluoresceins,
pubmed-meshheading:8035166-Membrane Potentials,
pubmed-meshheading:8035166-Models, Biological,
pubmed-meshheading:8035166-Oocytes,
pubmed-meshheading:8035166-Potassium,
pubmed-meshheading:8035166-Potassium Channels,
pubmed-meshheading:8035166-Sodium,
pubmed-meshheading:8035166-Sodium-Potassium-Exchanging ATPase,
pubmed-meshheading:8035166-Xenopus laevis
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pubmed:year |
1994
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pubmed:articleTitle |
Access channel model for the voltage dependence of the forward-running Na+/K+ pump.
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pubmed:affiliation |
Department of Physiology and Biophysics, University of Health Sciences/Chicago Medical School, Illinois 60064.
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pubmed:publicationType |
Journal Article,
Research Support, U.S. Gov't, P.H.S.
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