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Incorporation of polyunsaturated fatty acids into lipids of rainbow trout hepatocytes.

Hepatocytes from 5- or 20 degrees C-acclimated rainbow trout (Salmo gairdneri) were incubated with [1-14C]oleic, -linoleic, or -linolenic acid. Both acclimation groups demonstrated greater incorporation of derivatives from linolenic and linoleic acids into phospholipids when assayed at 5 and 20 degrees C; few derivatives of oleic acid were formed. Cells from cold-acclimated trout, when assayed at 5 degrees C with linolenic acid, incorporated a large proportion of radioactivity into free fatty acids. Analysis of each lipid fraction revealed a relatively specific incorporation of certain fatty acids. For example, "dead end" elongation products of the three substrates were preferentially incorporated into neutral lipids, while delta 6 desaturation products of the three acids were retained in the free fatty acid fraction. Twenty-carbon acid derivatives of linoleic and linolenic acids were directed into the phospholipid fraction. Incorporation of the delta 5 desaturation products was temperature sensitive in cells from cold-acclimated but not warm-acclimated trout. The results suggest that selectivity of incorporation of specific fatty acids into phospholipids may be of importance in restructuring membranes of poikilotherms during thermal adaptation.