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Record 16 of 2925
Permeation of halide anions through phospholipid bilayers occurs by the solubility-diffusion mechanism
Author and Affiliation:
Paula, S.(University of California, Department of Chemistry and Biochemistry, Santa Cruz 95064, United States)
Volkov, A. G.
Deamer, D. W.
Abstract: Two alternative mechanisms are frequently used to describe ionic permeation of lipid bilayers. In the first, ions partition into the hydrophobic phase and then diffuse across (the solubility-diffusion mechanism). The second mechanism assumes that ions traverse the bilayer through transient hydrophilic defects caused by thermal fluctuations (the pore mechanism). The theoretical predictions made by both models were tested for halide anions by measuring the permeability coefficients for chloride, bromide, and iodide as a function of bilayer thickness, ionic radius, and sign of charge. To vary the bilayer thickness systematically, liposomes were prepared from monounsaturated phosphatidylcholines (PC) with chain lengths between 16 and 24 carbon atoms. The fluorescent dye MQAE (N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide) served as an indicator for halide concentration inside the liposomes and was used to follow the kinetics of halide flux across the bilayer membranes. The observed permeability coefficients ranged from 10(-9) to 10(-7) cm/s and increased as the bilayer thickness was reduced. Bromide was found to permeate approximately six times faster than chloride through bilayers of identical thickness, and iodide permeated three to four times faster than bromide. The dependence of the halide permeability coefficients on bilayer thickness and on ionic size were consistent with permeation of hydrated ions by a solubility-diffusion mechanism rather than through transient pores. Halide permeation therefore differs from that of a monovalent cation such as potassium, which has been accounted for by a combination of the two mechanisms depending on bilayer thickness.
Publication Date: Jan 01, 1998
Document ID:
20040172806
(Acquired Dec 09, 2004)
Subject Category: EXOBIOLOGY
Document Type: Journal Article
Publication Information: Biophysical journal (ISSN 0006-3495); Volume 74; 1; 319-27
Publisher Information: United States
Description: In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
NASA Terms: ANIONS; BROMIDES; CHLORIDES; DIFFUSION; HALIDES; IODIDES; LIPIDS; MEMBRANES; PERMEATING; SOLUBILITY; DYES; EXOBIOLOGY; KINETICS; MODELS; PERMEABILITY
Other Descriptors: BROMIDES/CHEMISTRY; CHLORIDES/CHEMISTRY; IODIDES/CHEMISTRY; LIPID BILAYERS; PHOSPHATIDYLCHOLINES/CHEMISTRY; ANIONS; DIFFUSION; FLUORESCENT DYES; KINETICS; MODELS, CHEMICAL; PERMEABILITY; QUINOLINIUM COMPOUNDS; SOLUBILITY; STRUCTURE-ACTIVITY RELATIONSHIP; SUPPORT, U.S. GOV'T, NON-P.H.S; NASA DISCIPLINE EXOBIOLOGY; NON-NASA CENTER
Availability Source: Other Sources
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