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Active ion transport in the renal proximal tubule. II. Ionic dependence of the Na pump
The dependence of Na pump activity on intracellular and extracellular Na+ and K+ was investigated using a suspension of rabbit cortical tubules that contained mostly (86%) proximal tubules. The ouabain- sensitive rate of respiration (QO2) was used to measure the Na pump activity of intact tubules, a...
Formato: | Texto |
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Lenguaje: | English |
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The Rockefeller University Press
1984
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2228748/ https://www.ncbi.nlm.nih.gov/pubmed/6094705 |
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collection | PubMed |
description | The dependence of Na pump activity on intracellular and extracellular Na+ and K+ was investigated using a suspension of rabbit cortical tubules that contained mostly (86%) proximal tubules. The ouabain- sensitive rate of respiration (QO2) was used to measure the Na pump activity of intact tubules, and the Na,K-ATPase hydrolytic activity was measured using lysed proximal tubule membranes. The dependence (K0.5) of the Na pump on intracellular Na+ was affected by the relative intracellular concentration of K+, ranging from approximately 10 to 15 mM at low K+ and increasing to approximately 30 mM as the intracellular K+ was increased. The Na pump had a K0.5 for extracellular K+ of 1.3 mM in the presence of saturating concentrations of intracellular Na+. Measurements of the Na,K-ATPase activity under comparable conditions rendered similar values for the K0.5 of Na+ and K+. The Na pump activity in the intact tubules saturated as a function of extracellular Na at approximately 80 mM Na, with a K0.5 of 30 mM. Since Na pump activity under these conditions could be further stimulated by increasing Na+ entry with the cationophore nystatin, these values pertain to the Na+ entry step and not to the Na+ dependence of the intracellular Na+ site. When tubules were exposed to different extracellular K+ concentrations and the intracellular Na+ concentration was subsaturating, the Na pump had an apparent K0.5 of 0.4 mM for extracellular K. Under normal physiological conditions, the Na pump is unsaturated with respect to intracellular Na+, and indirect analysis suggests that the proximal cell may have an intracellular Na+ concentration of approximately 35 mM. |
format | Text |
id | pubmed-2228748 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 1984 |
publisher | The Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-22287482008-04-23 Active ion transport in the renal proximal tubule. II. Ionic dependence of the Na pump J Gen Physiol Articles The dependence of Na pump activity on intracellular and extracellular Na+ and K+ was investigated using a suspension of rabbit cortical tubules that contained mostly (86%) proximal tubules. The ouabain- sensitive rate of respiration (QO2) was used to measure the Na pump activity of intact tubules, and the Na,K-ATPase hydrolytic activity was measured using lysed proximal tubule membranes. The dependence (K0.5) of the Na pump on intracellular Na+ was affected by the relative intracellular concentration of K+, ranging from approximately 10 to 15 mM at low K+ and increasing to approximately 30 mM as the intracellular K+ was increased. The Na pump had a K0.5 for extracellular K+ of 1.3 mM in the presence of saturating concentrations of intracellular Na+. Measurements of the Na,K-ATPase activity under comparable conditions rendered similar values for the K0.5 of Na+ and K+. The Na pump activity in the intact tubules saturated as a function of extracellular Na at approximately 80 mM Na, with a K0.5 of 30 mM. Since Na pump activity under these conditions could be further stimulated by increasing Na+ entry with the cationophore nystatin, these values pertain to the Na+ entry step and not to the Na+ dependence of the intracellular Na+ site. When tubules were exposed to different extracellular K+ concentrations and the intracellular Na+ concentration was subsaturating, the Na pump had an apparent K0.5 of 0.4 mM for extracellular K. Under normal physiological conditions, the Na pump is unsaturated with respect to intracellular Na+, and indirect analysis suggests that the proximal cell may have an intracellular Na+ concentration of approximately 35 mM. The Rockefeller University Press 1984-10-01 /pmc/articles/PMC2228748/ /pubmed/6094705 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 Active ion transport in the renal proximal tubule. II. Ionic dependence of the Na pump |
title | Active ion transport in the renal proximal tubule. II. Ionic dependence of the Na pump |
title_full | Active ion transport in the renal proximal tubule. II. Ionic dependence of the Na pump |
title_fullStr | Active ion transport in the renal proximal tubule. II. Ionic dependence of the Na pump |
title_full_unstemmed | Active ion transport in the renal proximal tubule. II. Ionic dependence of the Na pump |
title_short | Active ion transport in the renal proximal tubule. II. Ionic dependence of the Na pump |
title_sort | active ion transport in the renal proximal tubule. ii. ionic dependence of the na pump |
topic | Articles |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2228748/ https://www.ncbi.nlm.nih.gov/pubmed/6094705 |