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Na-K pump current in the Amphiuma collecting tubule
There is strong evidence supporting the hypothesis of an electrogenic Na-K pump in the basolateral membrane of several epithelia. Thermodynamic considerations and results in nonepithelial cells indicate that the current carried by the pump could be voltage dependent. In order to measure the pump cur...
Formato: | Texto |
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Lenguaje: | English |
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The Rockefeller University Press
1989
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2228957/ https://www.ncbi.nlm.nih.gov/pubmed/2607332 |
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collection | PubMed |
description | There is strong evidence supporting the hypothesis of an electrogenic Na-K pump in the basolateral membrane of several epithelia. Thermodynamic considerations and results in nonepithelial cells indicate that the current carried by the pump could be voltage dependent. In order to measure the pump current and to determine its voltage dependence in a tight epithelium, we have used the isolated perfused collecting tubule of Amphiuma and developed a technique for clamping the basolateral membrane potential (Vbl) through transepithelial current injection. The transcellular current was calculated by subtracting the paracellular current (calculated from the transepithelial conductance measured in the presence of luminal amiloride) from the total transepithelial current. Basolateral membrane current-voltage (I-V) curves were obtained in conditions where the ratio of the pump current to the total basolateral membrane current had been maximized by loading the cells with Na+ (exposure to low-K+ bath), and by blocking the basolateral K+ conductance with barium. The pump current was defined as the difference of the current across the basolateral membrane measured before and 10-15 s after the addition of strophanthidin (20 microM) to the bath solution. With a bath solution containing 3 mM K+, the pump current was nearly constant in the Vbl range of -20 to -80 mV (52 +/- 5 microA.cm-2 at -60 mV) but showed a marked voltage dependence at higher negative Vbl (pump current decreased to 5 +/- 9 microA.cm-2 at -180 mV). In a 1.0 mM K bath, the shape of the pump I-V curve was similar but the amplitude of the current was decreased (24 +/- 4 microA.cm-2 at -60 mV). In a 0.1 mM K bath, the pump current was not significantly different from 0. Our results indicate that the basolateral Na-K pump generates a current which depends on the extracellular potassium concentration. With physiological peritubular concentration of K+ and in the physiological range of potential, the pump activity, measured as the pump-generated current, was independent of the membrane potential. |
format | Text |
id | pubmed-2228957 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 1989 |
publisher | The Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-22289572008-04-23 Na-K pump current in the Amphiuma collecting tubule J Gen Physiol Articles There is strong evidence supporting the hypothesis of an electrogenic Na-K pump in the basolateral membrane of several epithelia. Thermodynamic considerations and results in nonepithelial cells indicate that the current carried by the pump could be voltage dependent. In order to measure the pump current and to determine its voltage dependence in a tight epithelium, we have used the isolated perfused collecting tubule of Amphiuma and developed a technique for clamping the basolateral membrane potential (Vbl) through transepithelial current injection. The transcellular current was calculated by subtracting the paracellular current (calculated from the transepithelial conductance measured in the presence of luminal amiloride) from the total transepithelial current. Basolateral membrane current-voltage (I-V) curves were obtained in conditions where the ratio of the pump current to the total basolateral membrane current had been maximized by loading the cells with Na+ (exposure to low-K+ bath), and by blocking the basolateral K+ conductance with barium. The pump current was defined as the difference of the current across the basolateral membrane measured before and 10-15 s after the addition of strophanthidin (20 microM) to the bath solution. With a bath solution containing 3 mM K+, the pump current was nearly constant in the Vbl range of -20 to -80 mV (52 +/- 5 microA.cm-2 at -60 mV) but showed a marked voltage dependence at higher negative Vbl (pump current decreased to 5 +/- 9 microA.cm-2 at -180 mV). In a 1.0 mM K bath, the shape of the pump I-V curve was similar but the amplitude of the current was decreased (24 +/- 4 microA.cm-2 at -60 mV). In a 0.1 mM K bath, the pump current was not significantly different from 0. Our results indicate that the basolateral Na-K pump generates a current which depends on the extracellular potassium concentration. With physiological peritubular concentration of K+ and in the physiological range of potential, the pump activity, measured as the pump-generated current, was independent of the membrane potential. The Rockefeller University Press 1989-09-01 /pmc/articles/PMC2228957/ /pubmed/2607332 Text en This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/). |
spellingShingle | Articles Na-K pump current in the Amphiuma collecting tubule |
title | Na-K pump current in the Amphiuma collecting tubule |
title_full | Na-K pump current in the Amphiuma collecting tubule |
title_fullStr | Na-K pump current in the Amphiuma collecting tubule |
title_full_unstemmed | Na-K pump current in the Amphiuma collecting tubule |
title_short | Na-K pump current in the Amphiuma collecting tubule |
title_sort | na-k pump current in the amphiuma collecting tubule |
topic | Articles |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2228957/ https://www.ncbi.nlm.nih.gov/pubmed/2607332 |