The sheep erythrocyte membrane: A membrane with a particular lipid composition

LAURA BAKÁS; VANESA HERLAX; SABINA MATÉ; R. VAZQUEZ

Salta

Congreso; XXXIX Reunion Anual Sociedad Argentina de Biofísica (SAB); 2010

In mammals, phosphatidylcholine (PC) is generally the most abundant erythrocyte membrane phospholipid. However, there is a striking deviation in ruminants, because their erythrocyte membranes are particularly deficient in PC. Instead, they contain high levels of sphigomyelin (SM). A second unique aspect of ruminant erythrocyte membranes is the presence of N-acylated aminophospholipids, and an extreme asymmetry in phosphatidylethanolamine. The unique phospholipid composition of sheep erythrocytes appears as an evolutionary adaptation to tolerate the lytic effects of anti-phospholipid antibodies generated by  ruminal ciliates, parasites necessary for this group of mammals. SM association with cholesterol (CHO) is relevant in determining lipid conformational order and packing of membranes. On the other hand, these SM-CHO domains are related with the insolubility of membranes by detergents like Triton X100. However, by mass spectroscopy analysis the SM pattern of ghost sheep erythrocytes showed, surprisingly, that  the main SM species are long and unsaturated SMs,  SM 24:1,  represents  42 % of total SM, followed by  SM 24:2 (10%), SM 24:0 (7%), while SM 16:0 content reaches only  20%. These findings were surprisingly because the more common natural form of SM contain saturated hydrocarbon chains (SM 16:0) .  Taking into account these particularities in the lipid composition of rumiants erythrocytes, in this work, we present a biophysical characterization of sheep erythrocytes membranes, obtained by studies of protein interaction, detergents solubilization, cholesterol extraction with cyclodextrin and measurements of Laurdan Generalized Polarization (GP) obtained from images taken by a two-photon microscopy.