INVOLVEMENT OF PHOSPHOLIPID MOLECULAR-SPECIES IN CONTROLLING STRUCTURAL ORDER OF VERTEBRATE BRAIN SYNAPTIC-MEMBRANES DURING THERMAL EVOLUTION

Fluorescence anisotropy parameter of [p-(6-phenyl)-1,3,5-hexatrienyl]p henyl-propionic acid (DPH-PA) and trimethylammoniumphenyl)-6-phenyl-1, 3,5-hexatriene (TMA-DPH) embedded in synaptic plasma membranes prepare d from brains of cold (5 degrees C) and warm (22 degrees C) adapted fi sh (Cyprinus carpio L.), rat (Rattus norvegicus) and bird (Branta cana densis), was studied. Fatty acid composition of total lipids as well a s molecular species composition of diacyl phosphatidylcholines and pho sphatidylethanolamines was also determined. The amount of long-chain p olyunsaturated fatty acids decreased with increasing body temperature. There was a near-complete compensation of membrane structural order f or environmental/body temperature over the evolutionary scale as seen by DPH-PA. Using TMA-DPH, the compensation was partial with rat and bi rd. Since DPH-PA and TMA-DPH differ in their charges, it is proposed, that the former reported membrane regions rich in cationic or zwitteri onic (neutral) phospholipids and the latter, membrane regions rich in negatively charged phospholipids in the synaptic plasma membranes. Man y different molecular species (20-25) of diacyl phosphatidylcholines a nd diacyl phosphatidylethanolamines were identified. The level of 16:0 /22:6 phosphatidylcholine decreased while disaturated phosphatidylchol ines increased with increase of environmental/body temperature from th e fish through the bird. Level of 1-monoenoic, 2-polyenoic phosphatidy lethanolamines also decreased with an increase in environmental/body t emperature. Experiments using vesicles made of mixed synthetic phospha tidylcholine vesicles (16:0/16:0, 16:0/18:1, 16:0/22:6 in various prop ortions) showed that increase in disaturated phosphatidylcholine speci es does not explain the observed complete adjustment of membrane struc tural order in synaptic plasma membranes. Change in level of 1-monoeno ic, 2-polyenoic phosphatidylethanolamines might be one of the factors involved in controlling the biophysical properties of the membrane acc ording to the temperature.