Study on membrane fluidity and erythrocyte aggregation in equine, bovine and human species.

The aim of the present paper is to analyze whether membrane fluidity can be predicted from its lipid composition and to assay the possible relationship between such variable and the aggregating properties of erythrocytes from equine, bovine and human species due to the widely acknowledged differences in their tendency to form aggregates. The main difference between phospholipids from plasma membrane in these species lies in the concentration levels of sphyngomyelin (SM) and phosphatidilcoline (PC); more precisely, in the external hemilayer of the lipid bilayer. Membrane fluidity was estimated by the fluorescence polarization method, while erythrocyte aggregation was assessed by an optical method. According to our results, bovine erythrocytes containing high SM and low PC levels, presented the highest anisotropy value as well as an imperceptible aggregation value. Equine erythrocytes, which contain a considerable PC percentage and scarce SM levels, showed the lowest anisotropy value and the highest values of the aggregation parameters. Human erythrocytes presented intermediate values for both properties. Our hypothesis claims that the phospholipid composition would constitute one of the factors determining erythrocyte membrane fluidity and also taking part in the different aggregation tendency shown by equine, bovine and human species.