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Low CO2 permeability of cholesterol-containing liposomes detected by stopped-flow fluorescence spectroscopy

Tsiavaliaris, Georgios and Itel, Fabian and Hedfalk, Kristina and Al-Samir, Samer and Meier, Wolfgang and Gros, Gerolf and Endeward, Volker. (2015) Low CO2 permeability of cholesterol-containing liposomes detected by stopped-flow fluorescence spectroscopy. FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 29 (5). pp. 1780-1793.

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Official URL: http://edoc.unibas.ch/41923/

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Abstract

Here we ask the following: 1) what is the CO2 permeability (Pco2) of unilamellar liposomes composed of l-α-phosphatidylcholine (PC)/l-α-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 Pco2? Presently, a drastic discrepancy exists between the answers to these two questions obtained from mass-spectrometric (18)O-exchange measurements (Chol reduces Pco2 100-fold, AQP1 increases Pco2 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 (pCO2) 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 Pco2 = 0.01cm/s, and Chol-free vesicles exhibit ∼1 cm/s, and 2) the Pco2 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 Pco2 that can be raised when functionally necessary by incorporating protein-gas channels such as AQP1.
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Makromolekulare Chemie (Meier)
05 Faculty of Science > Departement Chemie
UniBasel Contributors:Itel, Fabian and Meier, Wolfgang P.
Item Type:Article, refereed
Article Subtype:Research Article
ISSN:0892-6638
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:30 Jun 2016 11:03
Deposited On:21 Apr 2016 13:33

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