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- Itel, F., et al.
(författare)
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CO2 permeability of cell membranes is regulated by membrane cholesterol and protein gas channels
- 2012
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Ingår i: Faseb Journal. - : Wiley. - 0892-6638 .- 1530-6860. ; 26:12, s. 5182-5191
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Tidskriftsartikel (refereegranskat)abstract
- Recent observations that some membrane proteins act as gas channels seem surprising in view of the classical concept that membranes generally are highly permeable to gases. Here, we study the gas permeability of membranes for the case of CO2, using a previously established mass spectrometric technique. We first show that biological membranes lacking protein gas channels but containing normal amounts of cholesterol (30-50 mol% of total lipid), e.g., MDCK and tsA201 cells, in fact possess an unexpectedly low CO2 permeability (PCO2) of similar to 0.01 cm/s, which is 2 orders of magnitude lower than the PCO2 of pure planar phospholipid bilayers (similar to 1 cm/s). Phospholipid vesicles enriched with similar amounts of cholesterol also exhibit PCO2 approximate to 0.01 cm/s, identifying cholesterol as the major determinant of membrane PCO2. This is confirmed by the demonstration that MDCK cells depleted of or enriched with membrane cholesterol show dramatic increases or decreases in PCO2, respectively. We demonstrate, furthermore, that reconstitution of human AQP-1 into cholesterol-containing vesicles, as well as expression of human AQP-1 in MDCK cells, leads to drastic increases in PCO2, indicating that gas channels are of high functional significance for gas transfer across membranes of low intrinsic gas permeability.-Itel, F., Al-Samir, S., Oberg, F., Chami, M., Kumar, M., Supuran, C. T., Deen, P. M. T., Meier, W., Hedfalk, K., Gros, G., Endeward, V. CO2 permeability of cell membranes is regulated by membrane cholesterol and protein gas channels. FASEB J. 26, 5182-5191 (2012). www.fasebj.org
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| 2. |
- Tsiavaliaris, G., et al.
(författare)
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Low CO2 permeability of cholesterol-containing liposomes detected by stopped-flow fluorescence spectroscopy
- 2015
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Ingår i: Faseb Journal. - : Wiley. - 0892-6638 .- 1530-6860. ; 29:5, s. 1780-1793
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Tidskriftsartikel (refereegranskat)abstract
- Here we ask the following: 1) what is the CO2 permeability (Pco(2)) of unilamellar liposomes composed of l--phosphatidylcholine (PC)/l--phosphatidylserine (PS) = 4:1 and containing cholesterol (Chol) at levels often occurring in biologic membranes (50 mol%), and 2) does incorporation of the CO2 channel aquaporin (AQP)1 cause a significant increase in membrane Pco(2)? Presently, a drastic discrepancy exists between the answers to these two questions obtained from mass-spectrometric O-18-exchange measurements (Chol reduces Pco(2) 100-fold, AQP1 increases Pco(2) 10-fold) vs. from stopped-flow approaches observing CO2 uptake (no effects of either Chol or AQP1). A novel theory of CO2 uptake by vesicles predicts that in a stopped-flow apparatus this fast process can only be resolved temporally and interpreted quantitatively, if 1) a very low CO2 partial pressure (pCO(2)) is used (e.g., 18 mmHg), and 2) intravesicular carbonic anhydrase (CA) activity is precisely known. With these prerequisites fulfilled, we find by stopped-flow that 1) Chol-containing vesicles possess a Pco(2) = 0.01cm/s, and Chol-free vesicles exhibit approximate to 1 cm/s, and 2) the Pco(2) of 0.01 cm/s is increased 10-fold by AQP1. Both results agree with previous mass-spectrometric results and thus resolve the apparent discrepancy between the two techniques. We confirm that biologic membranes have an intrinsically low Pco(2) that can be raised when functionally necessary by incorporating protein-gas channels such as AQP1.Tsiavaliaris, G., Itel, F., Hedfalk, K., Al-Samir, S., Meier, W., Gros, G., Endeward, V. Low CO2 permeability of cholesterol-containing liposomes detected by stopped-flow fluorescence spectroscopy.
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