HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Costa, P F Articles by Ferreira, K G Search for Related Content PubMed PubMed Citation Articles by Costa, P F Articles by Ferreira, K G

Departamento de Fisiologia, Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Oeiras, Portugal.

1. A method of estimating absolute ionic permeability coefficients which does not depend on the use of impermeant substitutes is reported. 2. The method is based on a pump leak model of the Xenopus laevis oocyte membrane. The procedure consists of measuring, in the same experiment, the pump current and the currents generated under voltage clamp by the partial substitution of one or two ions at a time. For each experimental condition, the measured currents are substituted in a Goldman-Hodgkin-Katz type equation with two unknowns (the permeability coefficients). The set of equations thus generated enables the computation of all the ionic permeability coefficients. 3. The Xenopus oocyte membrane (stages IV and V, Dumont, 1972) has been found to be permeable to conventional ion substitutes such as N-methyl-D-glucamine (NMG), sulphate, isethionate and gluconate. 4. The values for sodium, potassium and chloride permeability coefficients obtained from sixty-eight pooled experiments were, respectively, 5.44, 17.41 and 1.49 x 10(-8) cm s-1. 5. The diffusional currents for sodium, potassium and chloride computed from the experiments referred to above were, respectively, -1.16, 0.69 and -0.038 microA cm-2. 6. A stoichiometry of the Na+-K+ pump exchange of 3/1.8 was computed. 7. The intracellular concentrations of sodium, potassium and chloride ions, as determined by ion-selective microelectrodes, were, respectively, 10.1 +/- 0.66 mM (n = 12), 109.5 +/- 3.3 mM (n = 13) and 37.7 +/- 1.18 mM (n = 19), corresponding to equilibrium potentials of 61, -95 and -28 mV. 8. Since chloride is not at equilibrium across the membrane, we propose that there is an inward uphill Cl- transport.

This article has been cited by other articles:

				P. van Nierop, A. Keramidas, S. Bertrand, J. van Minnen, Y. Gouwenberg, D. Bertrand, and A. B. Smit Identification of Molluscan Nicotinic Acetylcholine Receptor (nAChR) Subunits Involved in Formation of Cation- and Anion-Selective nAChRs J. Neurosci., November 16, 2005; 25(46): 10617 - 10626. [Abstract] [Full Text] [PDF]

				F. E. Baird, K. J. Beattie, A. R. Hyde, V. Ganapathy, M. J. Rennie, and P. M. Taylor Bidirectional substrate fluxes through the System N (SNAT5) glutamine transporter may determine net glutamine flux in rat liver J. Physiol., September 1, 2004; 559(2): 367 - 381. [Abstract] [Full Text] [PDF]

				S. L. Ingram and S. G. Amara Arachidonic Acid Stimulates a Novel Cocaine-Sensitive Cation Conductance Associated with the Human Dopamine Transporter J. Neurosci., January 15, 2000; 20(2): 550 - 557. [Abstract] [Full Text] [PDF]

				A. Galli, C.I. Petersen, M. deBlaquiere, R.D. Blakely, and L.J. DeFelice Drosophila Serotonin Transporters Have Voltage-Dependent Uptake Coupled to a Serotonin-Gated Ion Channel J. Neurosci., May 15, 1997; 17(10): 3401 - 3411. [Abstract] [Full Text] [PDF]

				M. S. Sonders, S.-J. Zhu, N. R. Zahniser, M. P. Kavanaugh, and S. G. Amara Multiple Ionic Conductances of the Human Dopamine Transporter: The Actions of Dopamine and Psychostimulants J. Neurosci., February 1, 1997; 17(3): 960 - 974. [Abstract] [Full Text] [PDF]