Homeoviscous adaptation of different membranes in the brain of an air-breathing indian teleost, Channa punctatus, during seasonal variation of environmental temperature

An in vivo ratio control mechanism for phospholipid homeostasis: evidence from lipidomic studies

While it is widely accepted that the lipid composition of eukaryotic membranes is under homeostatic control, the mechanisms through which cells sense lipid composition are still the subject of debate. It has been postulated that membrane curvature elastic energy is the membrane property that is regulated by cells, and that lipid composition is maintained by a ratio control function derived from the concentrations of type II and type 0 lipids, weighted appropriately. We assess this proposal by seeking a signature of ratio control in quantified lipid composition data obtained by electrospray ionization mass spectrometry from over 40 independent asynchronous cell populations. Our approach revealed the existence of a universal 'pivot' lipid, which marks the boundary between type 0 lipids and type II lipids, and which is invariant between different cell types or cells grown under different conditions. The presence of such a pivot species is a distinctive signature of the operation in vivo, in human cell lines, of a control function that is consistent with the hypothesis that membrane elastic energy is homeostatically controlled.

Regulation of membrane lipid bilayer structure during salinity adaptation: a study with the gill epithelial cell membranes of Oreochromis niloticus

A significant variation in the membrane fluidity (as assessed by DPH-fluorescence polarisation) and membrane lipid bilayer composition is noticed in the subcellular membranes of the gill epithelial cells of Oreochromis niloticus due to exposure of the fish to 1% saline water for 1 month. Also, a 70% enhanced activity of Na(+)-K(+)-ATPase in plasma membranes and a 2.5-fold increase of glucose-6-phosphate dehydrogenase in microsomal membranes are recorded in the treated fish. The changed membrane structure and fluidity along with the changed enzymatic activity of Na(+)-K(+)-ATPase help the influx the Na(+) rather than the efflux of K(+) through the gill epithelial cells during salinity adaptation.

Docosahexaenoic acid-containing phospholipid molecular species in brains of vertebrates

The fatty acid composition of phospholipids and the contents of docosahexaenoic acid (DHA)-containing diacyl phosphatidylcholine and diacyl phosphatidylethanolamine molecular species were determined from brains of five fresh-water fish species from a boreal region adapted to 5 degrees C, five fresh-water fish species from a temperate region acclimated to 5 degrees C, five fresh-water fish species from a temperate region acclimated to 20 degrees C, and three fresh water fish species from a subtropic region adapted to 25-26 degrees C, as well as six mammalian species and seven bird species. There was little difference in DHA levels of fish brains from the different thermal environments; mammalian and bird brain phospholipids contained a few percentage points less DHA than those of the fish investigated. Molecular species of 22:6/22:6, 22:6/20:5, 22:6/20:4, 16:0/22:6, 18:0/22:6, and 18:1/22:6 were identified from all brain probes, and 16:0/22:6, 18:0/22:6, and 18:1/22:6 were the dominating species. Cold-water fish brains were rich in 18:1/22:6 diacyl phosphatidylethanolamine (and, to a lesser degree, in diacyl phosphatidylcholine), and its level decreased with increasing environmental/body temperature. The ratio of 18:0/22:6 to 16:0/22:6 phosphatidylcholine and phosphatidylethanolamine was inversely related to body temperature. Phospholipid vesicles from brains of cold-acclimated fish were more fluid, as assessed by using a 1, 6-diphenyl-1,3,5-hexatriene fluorescent probe, than those from bird brains, but the fluidities were almost equal at the respective body temperatures. It is concluded that the relative amounts of these molecular species and their ratios to each other are the major factors contributing to the maintenance of proper fluidity relationships throughout the evolutionary chain as well as helping to maintain important brain functions such as signal transduction and membrane permeability.

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.