Rapid changes in the phospholipid composition of gill membranes during thermal acclimation of the rainbow trout, Salmo gairdneri.

The phospholipid composition of gill tissue was determined in rainbow trout (Salmo gairdneri) undergoing thermal acclimation between 5 degrees C and 20 degrees C for a period of up to 28 days. Proportions of phosphatidylethanolamine (PE) and cardiolipin (CL) increased during cold acclimation and decreased during warm acclimation; proportions of phosphatidylcholine (PC) changed in the opposite direction (i.e., decreased during cold acclimation). In contrast, levels of phosphatidylserine, -inositol, and sphingomyelin did not vary significantly. Thermal modulation of headgroup composition occurred rapidly as reflected by changes in the ratio of PC-to-PE, which rose significantly from 2.40 +/- 0.09 to 2.92 +/- 0.09 within 72 h of transfer from 5 to 20 degrees C; adaptation to 5 degrees C was equally rapid. Proportions of PE changed more rapidly than those of PC during cold adaptation, whereas the opposite was true during warm acclimation. Both the time course and the direction of the observed changes in phospholipid composition suggest that such adjustments may contribute to the homeoviscous regulation of membrane properties, particularly during the initial stages of thermal adaptation.