Fatty acyl chain composition in the determination of renal membrane order.

The relative roles of phospholipid fatty acyl chain length and phospholipid fatty acyl chain unsaturation in the determination of rat renal brush border membrane order were examined using multilamellar liposomes. Exposure of brush border membranes to sphingomyelinase resulted in a time- and concentration-dependent decrement in sphingomyelin content. Liposomes prepared from lipid extracts of these membranes were reconstituted to defined phosphatidylcholine (PC)/sphingomyelin (SPH) ratios with pure synthetic PCs of defined chain length and degrees of unsaturation. Mixed-acid PCs from bovine liver, egg, and the rat renal brush border membrane were also examined. The steady state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) at 37 degrees C was used to reflect acyl chain packing. The steady state anisotropy of DPH in liposomes isolated from the rat renal brush border membrane averaged 0.205 +/- 0.001, n = 8. When liposomes were reconstituted to PC/SPH ratios of 1.1, 1.6, and 2.4 with saturated PCs of acyl chain length 16 to 22, differences in anisotropy between groups were not observed. However, when PCs containing unsaturated or mixed-acid fatty acyl chains were introduced, anisotropy decreased in a concentration dependent fashion. These data suggest that phospholipid fatty acyl chain unsaturation, but not acyl chain length, has a powerful influence on renal brush border membrane order and the PC/SPH ratio is an important determinant of renal membrane order by virtue of the unsaturated fatty acids normally present with these phospholipids.