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Diffusion of carbon dioxide through lipid bilayer membranes. Effects of carbonic anhydrase, bicarbonate, and unstirred layers
Diffusion of (14)C-labeled CO(2) was measured through lipid bilayer membranes composed of egg lecithin and cholesterol (1:1 mol ratio) dissolved in n-decane. The results indicate that CO(2), but not HCO(3-), crosses the membrane and that different steps in the transport process are rate limiting und...
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Formato: | Texto |
Lenguaje: | English |
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The Rockefeller University Press
1977
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2215341/ https://www.ncbi.nlm.nih.gov/pubmed/408462 |
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author | Gutknecht, J Bisson, MA Tosteson, FC |
author_facet | Gutknecht, J Bisson, MA Tosteson, FC |
author_sort | Gutknecht, J |
collection | PubMed |
description | Diffusion of (14)C-labeled CO(2) was measured through lipid bilayer membranes composed of egg lecithin and cholesterol (1:1 mol ratio) dissolved in n-decane. The results indicate that CO(2), but not HCO(3-), crosses the membrane and that different steps in the transport process are rate limiting under different conditions. In one series of experiments we studied one-way fluxes between identical solutions at constant pCO(2) but differing [HCO(3-)] and pH. In the absence of carbonic anhydrase (CA) the diffusion of CO(2) through the aqueous unstirred layers is rate limiting because the uncatalyzed hydration-dehydration of CO(2) is too slow to permit the high [HCO(3-)] to facilitate tracer diffusion through the unstirred layers. Addition of CA (ca. 1 mg/ml) to both bathing solutions causes a 10-100-fold stimulation of the CO(2) flux, which is proportional to [HCO(3-)] over the pH range 7-8. In the presence of CA the hydration- dehydration reaction is so fast that CO(2) transport across the entire system is rate limited by diffusion of HCO(3-) through unstirred layers. However, in the presence of CA when the ratio [HCO(3-) + CO(3=)]:[CO(2)] more than 1,000 (pH 9-10) the CO(2) flux reaches a maximum value. Under these conditions the diffusion of CO(2) through the membrane becomes rate limiting, which allows us to estimate a permeability coefficient of the membrane to CO(2) of 0.35 cm s(-1). In a second series of experiments we studied the effects of CA and buffer concentration on the net flux of CO(2). CA stimulates the net CO(2) flux in well buffered, but no in unbuffered, solutions. The buffer provides a proton source on the upstream side of the membrane and proton sink on the downstream side, thus allowing HCO(3-) to facilitate the net transport of CO(2) through the unstirred layers. |
format | Text |
id | pubmed-2215341 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 1977 |
publisher | The Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-22153412008-04-23 Diffusion of carbon dioxide through lipid bilayer membranes. Effects of carbonic anhydrase, bicarbonate, and unstirred layers Gutknecht, J Bisson, MA Tosteson, FC J Gen Physiol Articles Diffusion of (14)C-labeled CO(2) was measured through lipid bilayer membranes composed of egg lecithin and cholesterol (1:1 mol ratio) dissolved in n-decane. The results indicate that CO(2), but not HCO(3-), crosses the membrane and that different steps in the transport process are rate limiting under different conditions. In one series of experiments we studied one-way fluxes between identical solutions at constant pCO(2) but differing [HCO(3-)] and pH. In the absence of carbonic anhydrase (CA) the diffusion of CO(2) through the aqueous unstirred layers is rate limiting because the uncatalyzed hydration-dehydration of CO(2) is too slow to permit the high [HCO(3-)] to facilitate tracer diffusion through the unstirred layers. Addition of CA (ca. 1 mg/ml) to both bathing solutions causes a 10-100-fold stimulation of the CO(2) flux, which is proportional to [HCO(3-)] over the pH range 7-8. In the presence of CA the hydration- dehydration reaction is so fast that CO(2) transport across the entire system is rate limited by diffusion of HCO(3-) through unstirred layers. However, in the presence of CA when the ratio [HCO(3-) + CO(3=)]:[CO(2)] more than 1,000 (pH 9-10) the CO(2) flux reaches a maximum value. Under these conditions the diffusion of CO(2) through the membrane becomes rate limiting, which allows us to estimate a permeability coefficient of the membrane to CO(2) of 0.35 cm s(-1). In a second series of experiments we studied the effects of CA and buffer concentration on the net flux of CO(2). CA stimulates the net CO(2) flux in well buffered, but no in unbuffered, solutions. The buffer provides a proton source on the upstream side of the membrane and proton sink on the downstream side, thus allowing HCO(3-) to facilitate the net transport of CO(2) through the unstirred layers. The Rockefeller University Press 1977-06-01 /pmc/articles/PMC2215341/ /pubmed/408462 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 Gutknecht, J Bisson, MA Tosteson, FC Diffusion of carbon dioxide through lipid bilayer membranes. Effects of carbonic anhydrase, bicarbonate, and unstirred layers |
title | Diffusion of carbon dioxide through lipid bilayer membranes. Effects of carbonic anhydrase, bicarbonate, and unstirred layers |
title_full | Diffusion of carbon dioxide through lipid bilayer membranes. Effects of carbonic anhydrase, bicarbonate, and unstirred layers |
title_fullStr | Diffusion of carbon dioxide through lipid bilayer membranes. Effects of carbonic anhydrase, bicarbonate, and unstirred layers |
title_full_unstemmed | Diffusion of carbon dioxide through lipid bilayer membranes. Effects of carbonic anhydrase, bicarbonate, and unstirred layers |
title_short | Diffusion of carbon dioxide through lipid bilayer membranes. Effects of carbonic anhydrase, bicarbonate, and unstirred layers |
title_sort | diffusion of carbon dioxide through lipid bilayer membranes. effects of carbonic anhydrase, bicarbonate, and unstirred layers |
topic | Articles |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2215341/ https://www.ncbi.nlm.nih.gov/pubmed/408462 |
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