STRUCTURAL ORDER OF MEMBRANES AND COMPOSITION OF PHOSPHOLIPIDS IN FISH BRAIN-CELLS DURING THERMAL ACCLIMATIZATION

A comparison of the structural orders of membranes of a mixed brain-ce ll population isolated from Cyprinus carpio L. acclimated to either su mmer (23-25 degrees C) or winter (5 degrees C) revealed a high degree of compensation (80%) for temperature, as assayed by electron spin res onance spectroscopy. The cells rapidly forget their thermal history an d adjust the physical properties of the membranes when shifted to the other extreme of temperature either in vivo or in vitro. Phospholipids separated from both types of animal exhibit only around 10% compensat ion. Arachidonic and docosahexaenoic acids are the major polyunsaturat ed fatty acids in the brains, but the fatty acid composition of the br ain total phospholipids does not vary with adaptation to temperature. Separation of phosphatidylcholines and phosphatidylethanolamines into molecular species revealed a 2- to 3-fold accumulation of 18:1/22:6, 1 8:1/20:4, and 18:1/18:1 species in the latter; 18:0/22:6 Showed an opp osite tendency. Molecular species composition of phosphatidylcholines did not vary with the temperature. The same trends of changes were see n with brains of freshwater fish from subtropical (Catla catla L.) or boreal (Acerina cernua) regions. It is concluded that the gross amount of docosahexaenoic acid (22:6) plays only a minor role in adjusting t he membrane physical properties to temperature. Factors other than lip ids might be involved in the adaptation processes. Due to their specif ic molecular architecture, molecules such as 18:1/22:6, 18:1/20:4, or 18:1/18:1 phosphatidylethanolamine might prevent the contraction of me mbranes in the cold and may provide an environment for some other comp onents involved in the temperature regulation of physical properties o f nerve cell membranes.