Regulation of membrane lipid bilayer structure during seasonal variation: a study on the brain membranes of Clarias batrachus.

(1) A significant seasonal variation in the membrane fluidity (as sensed by DPH-fluorescence polarization), membrane lipid components (phospholipid and neutral lipid), fatty acid composition of membrane phospholipid (phosphatidylcholine, phosphatidylethanolamine and sphingomyelin), positional distribution of fatty acids at Sn-1 and Sn-2 position of phosphatidyl-choline and -ethanolamine is noticed in the brain membranes (myelin, synaptosomes, and mitochondria) of a tropical air breathing teleost, Clarias batrachus. (2) A 'partial compensation' of membrane fluidity during seasonal adaptation is observed in myelin and mitochondria membrane fractions. Synaptosomes membrane fraction exhibits a different response. Depletion (about 15-70%) of membrane lipid components (phospholipid, cholesterol, diacylglycerol and triacylglycerol) per unit of membrane protein is the characteristic feature of summer adaptation. An increase (about 20-100%) in the level of oleic acid and decrease (about 20-60%) in the level of stearic acid are almost common features in membrane phospholipid fractions of winter-adapted Clarias (3) From the tissue slice experiment it is evident that there is an activation of cellular phospholipase A2 at lower growth temperature and of cellular phospholipase A1 at higher growth temperature and this suggests the reorganization of molecular architecture of the membrane during seasonal adaptation. (4) Accumulation of oleic acid in Sn-1 position and polyunsaturated fatty acids in Sn-2 position of phosphatidylcholine and -ethanolamine during winter indicates an increase in the concentration of 1-monoenoic, 2-polyenoic molecular species of phospholipid in order to maintain the stability of membrane lipid bilayer.