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

Abstract

(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 phopholipase A 2 at lower growth temperature and of cellular phosphalipase A 1 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 phophatidyl-choline 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.