title: Lipid domains in plasma membranes from rat liver.
abstract: The existence of fluid and solid lipid domains in isolated rat-liver plasma membranes was evaluated using the fluorescent fatty acids trans-parinaric and cis-parinaric acid as probe molecules for solid and fluid membrane areas, respectively. The fluorescence probe 1,6-diphenyl-1,3,5-hexatriene indicated that a phase transition was present in the liver plasma membrane between 18 degrees C and 30 degrees C. At intermediate temperatures, cis-parinaric acid, which partitioned approximately equally into fluid and solid lipid areas, detected two lipid domains: the mole fractions of fluid and solid lipid domains at 24 degrees C were 0.32 and 0.68 while the mole fractions of cis-parinaric acid in each domain were 0.34 and 0.66, respectively. The dissociation constant, aqueous to membrane lipid partition coefficient, and bound to free ratio for trans-parinaric acid were 7.0 +/- 0.7 microM, 4.0 +/- 0.6 x 10(6), and 83:17, respectively. The affinity of the membrane for cis-parinaric acid was twofold lower than for trans-parinaric acid. The trans-parinaric acid partitioned preferentially into solid lipid, Ksp/f = 3.30, while the cis-parinaric acid partitioned equally between fluid and solid phases Ksp/f = 0.92. Thus, the data demonstrate the coexistence of fluid and solid domains in rat liver plasma membranes.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D008297:Male; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000302:isolation & purification*; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains; D013050:Spectrometry, Fluorescence; D013237:Stereoisomerism
chemical_list: D005231:Fatty Acids, Unsaturated; D008563:Membrane Lipids; C013641:parinaric acid