Lateral diffusion of lipids in sarcoplasmic reticulum membranes is area limited

Abstract

Scandella et al.¹ used the technique of electron spin resonance to investigate lateral lipid diffusion in the membrane of sarcoplasmic reticulum from skeletal muscle. Their results suggested that lipids are free to diffuse within the plane of the membrane at rates comparable with those in isolated phospholipid bilayer systems of similar composition^2–4. However, their study¹ was carried out at temperatures between 50 and 70 °C. I have therefore now carried out similar studies, but at physiological temperatures and using fatty acid analogue spin labels. My results show absence of spin-exchange interaction at spin label concentrations below 2–4 mol %. This suggests the existence of diffusion barriers in the plane of the membrane which separate the lipids into clusters containing, on average, about 50 phospholipid molecules.