The incorporation of unsaturated fatty acids of the n‐9, n‐6, and n‐3 families into individual phospholipids by isolated hepatocytes of thermally‐acclimated rainbow trout, Salmo gairdneri

Abstract

Rates of incorporation of 1‐¹⁴C‐oleic (18:1n9), ‐linoleic (18:2n6), and ‐linolenic (18:3n3) acids into individual phosphatides were determined in isolated hepatocytes from cold (5°C)‐ and warm (20°C)‐acclimated rainbow trout, Salmo gairdneri. Fatty acid incorporation into phosphatidylcholine (PC) exceeded that into all other phospholipids, but at assay and acclimation temperatures of 5°C, incorporation into phosphatidylethanolamine (PE) was generally intermediate between that of PC and the remaining phosphatides. Specific radioactivities (ratios of percentage isotope incorporation‐to‐mole percentage of phosphatide) were consistently less than one for both PC and PE, and greater than one for phosphatidic acid (PA), lysophosphatidylcholine (LPC), phosphatidylserine (PS), and cardiolipin (CL). For PS, specific radioactivities were greater in cold‐ than warm‐acclimated trout, and greater at 5°C than 20°C. Rates of oleate incorporation were generally higher, and rates of incorporation of 18:2 and 18:3 lower in cold‐ than warm‐acclimated trout. Most phospholipids demonstrated a clear preference for the incorporation of 18:2 when assayed at 20°C; however, at 5°C the incorporation of 18:2 was reduced and 18:3 was generally the preferred substrate A reduction in assay temperature from 20°C to 5°C also shifted the incorporation of 18:2 away from PC into PS and PA. These data were interpreted to indicate 1) a cold‐induced activation of PS metabolism, possibly resulting in elevated levels of PE; 2) lower rates of general acyl group turnover in animals acclimated to 5°C than 20°C; 3) a specificity to the acclimation response that favors the incorporation at cold temperatures of polyunsaturated fatty acids, but not the parent acids from which they are derived; and 4) the participation of a deacylation‐reacylation cycle in the metabolism of phospholipids, particularly at cold temperatures.