Fatty acid composition of the ingested food only slightly affects physicochemical properties of liver total phospholipids and plasma membranes in cold-adapted freshwater fish

摘要

The fatty acid content, fatty acid molecular species composition, and fluidity of phospholipid vesicles and plasma membranes of livers of fish feeding on phytoplankton (silver carp, Hypophthalmichthys molitrix), zooplankton, (big head carp, Hypophtalmitrix nobilis), higher plants, (grass carp, Ctenopharyngodon idella), and omnivorous fish, (common carp, Cyprinus carpio), adapted to reduced temperatures, were studied. Levels of long chain polyunsaturated fatty acids (PUFAs) were highest in silver and big head carp and lowest in common carp. Differences in long chain PUFAs were poorly reflected in fluidity, determined by fluorescence anisotropy of 1,6-diphenyl 1,3,5-hexatriene or rotational correlation time of 16-doxyl- stearic acid, of phospholipidvesicles. Phospholipid vesicles of C. carpio and C. idella proved to be slightly more rigid than of H. molitrix and H. nobilis below 15deg C. These differences were not seen with isolated plasma membranes assessed with 1,6-diphenyl 1,3,5-hexatriene. Usingelectron spin resonance spectroscopy plasma membranes from H. molitrix proved to be more fluid than those from C. carpio below 15deg C. Phosphatidylethanolamines were abundant in 1-monounsaturated, 2-polyunsaturated (18:1/22:6, 18:1/20:4) species with H. molitrix and H. nobilis more rich in these species than C. carpio and C. idella. It is suggested that differences in fluidities of phospholipid vesicles below 15deg C is due to differences in levels of the above molecular species. In native membranes these differences may be masked by proteins and other membrane components. It is also suggested that it is not the fatty acid composition of the ingested food but the specific response of the fish to temperature that is the most important factor controlling thephysicochemical properties of membranes during thermal adaptation.