Effects of an amphipathic drug on the rheological properties of the cell membrane

Sodium thiopental, as other amphiphilic molecules, interacts with the membr ane by inserting into the lipid bilayer and causing alterations of the memb rane properties such as curvature and hypotonic lysis resistance. But can i t modify the mechanical properties of the membrane? In the present work it was observed that sodium thiopental affected the membrane rheological prope rties by improving erythrocyte deformability; this effect resulted from a r eduction of both the elastic modulus and surface viscosity. In erythrocytes devoid of sialic acid after treatment with neuraminidase, sodium thiopenta l membrane concentration was significantly higher than in normal cells, sug gesting that drug access to the lipid bilayer be facilitated by the absence of the steric and electrostatic barrier of the glycocalyx negative charges . From a rheological point of view, desialated and normal cells showed the same response to the anesthetic as regards elastic modulus but in opposite direction if surface viscosity was considered. This finding supports the hy pothesis that sodium thiopental molecules enter the bilayer of desialated c ells in a higher proportion, as compared to the normal erythrocyte, promoti ng a disorganization that results in a greater inner friction. The changes in the rheological parameters, triggered by sodium thiopental, could be att ributed to the bilayer contribution to the membrane mechanical properties, either directly or through interaction between the bilayer and the cytoskel eton. (C) 1998 Academic Press.