Possible role of anisotropic membrane inclusions in stability of torocyte red blood cell daughter vesicles

The stability of torocyte red blood cell daughter endovesicles induced by octaethylene-glycol dodecylether (C12E8) was studied theoretically. In addition, the effects of C12E8 and tetraethylene-glycol dodecylether (C12E4) on physical properties of the red blood cell membrane were studied experimentally, using the electron spin resonance (ESR) technique. In the theoretical part, it was assumed that the stable vesicle shape corresponds to the minimum of its membrane free energy, which is the sum of the membrane bending energy and the contribution of the C12E8-induced membrane inclusions. We found that the torocytic vesicle shape may be stable due to quadrupolar ordering of the C12E8 anisotropic inclusions that are embedded in the vesicle membrane. It was also shown how a preference of the membrane inclusions for a specific membrane curvature might lead to their non-homogeneous lateral distribution. In the experimental part, it was shown that C12E4 drastically changes the proportions of the membrane lipid domains (characterized by different 'fluidity'), while C12E8 induces much smaller changes in the proportions of the domains. A possible relation between the difference in the effects of C12E8 and C12E4 on the membrane lipid domains, and their distribution between the membrane leaflets, is discussed. (C) 2002 Published by Elsevier Science B.V.