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The Permeability of Thin Lipid Membranes to Bromide and Bromine

Thin lipid (optically black) membranes were made from sheep red cell lipids dissolved in n-decane. The flux of Br across these membranes was measured by the use of tracer (82)Br. The unidirectional flux of Br (in 50–100 mM NaBr) was 1–3 x 10(-12) mole/cm(2)sec. This flux is more than 1000 times the...

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Autores principales: Gutknecht, John, Bruner, L. J., Tosteson, D. C.
Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 1972
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2203188/
https://www.ncbi.nlm.nih.gov/pubmed/5063846
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author Gutknecht, John
Bruner, L. J.
Tosteson, D. C.
author_facet Gutknecht, John
Bruner, L. J.
Tosteson, D. C.
author_sort Gutknecht, John
collection PubMed
description Thin lipid (optically black) membranes were made from sheep red cell lipids dissolved in n-decane. The flux of Br across these membranes was measured by the use of tracer (82)Br. The unidirectional flux of Br (in 50–100 mM NaBr) was 1–3 x 10(-12) mole/cm(2)sec. This flux is more than 1000 times the flux predicted from the membrane electrical resistance (>10(8) ohm-cm(2)) and the transference number for Br(-) (0.2–0.3), which was estimated from measurements of the zero current potential difference. The Br flux was not affected by changes in the potential difference imposed across the membrane (±60 mv) or by the ionic strength of the bathing solutions. However, the addition of a reducing agent, sodium thiosulfate (10(-3) M), to the NaBr solution bathing the membrane caused a 90% reduction in the Br flux. The inhibiting effect of S(2)O(3) (=) suggests that the Br flux is due chiefly to traces of Br(2) in NaBr solutions. As expected, the addition of Br(2) to the NaBr solutions greatly stimulated the Br flux. However, at constant Br(2) concentration, the Br flux was also stimulated by increasing the Br(-) concentration, in spite of the fact that the membrane was virtually impermeable to Br(-). Finally, the Br flux appeared to saturate at high Br(2) concentrations, and the saturation value was roughly proportional to the Br(-) concentration. These results can be explained by a model which assumes that Br crosses the membrane only as Br(2) but that rapid equilibration of Br between Br(2) and Br(-) occurs in the unstirred layers of aqueous solution bathing the two sides of the membrane. A consequence of the model is that Br(-) "facilitates" the diffusion of Br across the unstirred layers.
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spelling pubmed-22031882008-04-23 The Permeability of Thin Lipid Membranes to Bromide and Bromine Gutknecht, John Bruner, L. J. Tosteson, D. C. J Gen Physiol Article Thin lipid (optically black) membranes were made from sheep red cell lipids dissolved in n-decane. The flux of Br across these membranes was measured by the use of tracer (82)Br. The unidirectional flux of Br (in 50–100 mM NaBr) was 1–3 x 10(-12) mole/cm(2)sec. This flux is more than 1000 times the flux predicted from the membrane electrical resistance (>10(8) ohm-cm(2)) and the transference number for Br(-) (0.2–0.3), which was estimated from measurements of the zero current potential difference. The Br flux was not affected by changes in the potential difference imposed across the membrane (±60 mv) or by the ionic strength of the bathing solutions. However, the addition of a reducing agent, sodium thiosulfate (10(-3) M), to the NaBr solution bathing the membrane caused a 90% reduction in the Br flux. The inhibiting effect of S(2)O(3) (=) suggests that the Br flux is due chiefly to traces of Br(2) in NaBr solutions. As expected, the addition of Br(2) to the NaBr solutions greatly stimulated the Br flux. However, at constant Br(2) concentration, the Br flux was also stimulated by increasing the Br(-) concentration, in spite of the fact that the membrane was virtually impermeable to Br(-). Finally, the Br flux appeared to saturate at high Br(2) concentrations, and the saturation value was roughly proportional to the Br(-) concentration. These results can be explained by a model which assumes that Br crosses the membrane only as Br(2) but that rapid equilibration of Br between Br(2) and Br(-) occurs in the unstirred layers of aqueous solution bathing the two sides of the membrane. A consequence of the model is that Br(-) "facilitates" the diffusion of Br across the unstirred layers. The Rockefeller University Press 1972-04-01 /pmc/articles/PMC2203188/ /pubmed/5063846 Text en Copyright © 1972 by The Rockefeller University Press 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 Article
Gutknecht, John
Bruner, L. J.
Tosteson, D. C.
The Permeability of Thin Lipid Membranes to Bromide and Bromine
title The Permeability of Thin Lipid Membranes to Bromide and Bromine
title_full The Permeability of Thin Lipid Membranes to Bromide and Bromine
title_fullStr The Permeability of Thin Lipid Membranes to Bromide and Bromine
title_full_unstemmed The Permeability of Thin Lipid Membranes to Bromide and Bromine
title_short The Permeability of Thin Lipid Membranes to Bromide and Bromine
title_sort permeability of thin lipid membranes to bromide and bromine
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2203188/
https://www.ncbi.nlm.nih.gov/pubmed/5063846
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