Abstract
Rates of glycerol and fatty acid (18:0, 18:1, 18:3 and 20:4) incorporation into phosphatidylcholine (PC), phosphatidylethanolamine (PE) and triacylglycerol were measured in isolated hepatocytes of thermallyacclimated (5° C and 20° C) rainbow trout ( Salmo gairdneri) in order to assess the contribution(s) of the de novo and deacylation/reacylation pathways to the metabolism of membrane lipids. In PC, the effects of acclimation temperature were fatty acid dependent; for 18:0 and 20:4 n − 6 rates of fatty acid incorporation were greater in warm- than cold-acclimated trout, whereas the reverse was true for the incorporation of 18:1. In the case of both PE and triacylglycerol, unsaturated, but not saturated, fatty acids (18:0) were incorporated more rapidly by hepatocytes of cold- than warm-acclimated trout. For PC, ratios of fatty acid / glycerol incorporation were consistently lower than the corresponding ratios for phosphatidic acid regardless of the fatty acid, assay or acclimation temperature. In contrast, fatty acid / glycerol ratios for PE were higher than those for phosphatidic acid in (i) cold- compared to warm-acclimated trout and (ii) in assays conducted at 5°C compared to 20°C for cold-acclimated fish; in addition, ratios generally increased with the degree of unsaturation of the fatty acid in cold-acclimated trout. In the triacylglycerol fraction, fatty acid / glycerol ratios were greater than those for phosphatidic acid in warm-acclimated trout only, and were generally greater in warm- than cold-acclimated fish. These results were interpreted to indicate: (1) an increased contribution of the deacylation/reacylation cycle to the incorporation of unsaturated fatty acids into PE in cold- compared to warm-acclimated fish, and at 5° C compared to 20° C in cold-acclimated trout; and (2) a role for the deacylation/reacylation cycle in excluding the incorporation of unsaturated fatty acids into PC, particularly evident in warm-acclimated trout. The possibility that different metabolic mechanisms are operating to maintain the composition of PE at different temperatures is discussed.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA)/Lipids and Lipid Metabolism
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