Phospholipids, fatty acids and hemoglobin in rat erythrocytes under stress conditions (swimming at low temperature)

The phospholipid and fatty acid composition of rat erythrocytes was studied after stress exposure—swimming until drowning. This kind of stress was found to increase the content of phospholipids typical for the outer membrane layer (phosphatidylcholine by 13% and sphingomyelin by 23%). In contrast, the content of acid phospholipids, referring to the inner membrane layer, decreased (phosphatidylethanolamine by 16%, phosphatidylserine by 14% and monophosphoinositide by 23%). Our data indicate that under stress conditions the erythrocyte membrane undergoes certain structural changes, which appear to affect its functional properties. At the same time, the content of saturated and unsaturated fatty acids, as well as their “unsaturation index”, remain basically intact under the above stress conditions, probably, preserving functional properties of the erythrocyte membrane by compensating its impaired phospholipid structure. Based on the analysis of absorption spectra of lipid extracts, stress was established to induce a 2-fold spectrum enhancement in the heme-specific range of 390–410 nm. The appearance of heme in the extract indicates hemoglobin saponification induced by changes in pH of the erythrocyte internal environment. Indeed, during lipid extraction hemoglobin converts into a disordered state due to the effect not only of temperature and pH of the medium, but also of organic solvents, having a lower capacity to form hydrogen bonds than water. Probably, a small portion of phospholipids undergoes trans-esterification during their extraction from erythrocytes by the chloroform–methanol mixture.