Influence of Chain Ordering on the Selectivity of Dipalmitoylphosphatidylcholine Bilayer Membranes for Permeant Size and Shape

• Published in: Biophysical journal 1998-12, Vol.75 (6), p.2658-2671
• Main Authors: Xiang, Tian-Xiang, Anderson, Bradley D.
• Format: Article
• Language: English
• Subjects: 1,2-Dipalmitoylphosphatidylcholine - chemistry; Biophysical Phenomena; Biophysics; Carboxylic Acids - chemistry; Diffusion; In Vitro Techniques; Light; Lipid Bilayers - chemistry; Liposomes - chemistry; Magnetic Resonance Spectroscopy; Models, Chemical; Models, Molecular; Molecular Conformation; Permeability; Scattering, Radiation; Solubility; Surface Properties; Thermodynamics
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(98)77711-2

The effects of lipid chain packing and permeant size and shape on permeability across lipid bilayers have been investigated in gel and liquid crystalline dipalmitoylphosphatidylcholine (DPPC) bilayers by a combined NMR line-broadening/dynamic light scattering method using seven short-chain monocarboxylic acids (formic acid, acetic acid, propionic acid, butyric acid, valeric acid, isovaleric acid, and trimethylacetic acid) as permeants. The experimental permeability coefficients are compared with the predictions of a bulk solubility diffusion model in which the bilayer membrane is represented as a slab of bulk hexadecane. Deviations of the observed permeability coefficients ( P m) from the values predicted from solubility diffusion theory ( P o) lead to the determination of a correction factor, the permeability decrement f (= P m/ P o), to account for the effects of chain ordering. The natural logarithm of f has been found to correlate linearly with the inverse of the bilayer free surface area with slopes of 25 ± 2, 36 ± 3, 45 ± 8, 32 ± 12, 33 ± 4, 49 ± 12, and 75 ± 6 Å 2 for formic acid, acetic acid, propionic acid, butyric acid, valeric acid, isovaleric acid, and trimethylacetic acid, respectively. The slope, which measures the sensitivity of the permeability coefficient of a given permeant to bilayer chain packing, exhibits an excellent linear correlation ( r = 0.94) with the minimum cross-sectional area of the permeant and a poor correlation ( r = 0.59) with molecular volume, suggesting that in the bilayer interior the permeants prefer to move with their long principal axis along the bilayer normal. Based on these studies, a permeability model combining the effects of bilayer chain packing and permeant size and shape on permeability across lipid membranes is developed.