Stability and pH sensitivity of sulfatide-containing phosphatidylethanolamine small unilamellar vesicles

The bilayer stabilization effect of sulfatide and the pH sensitivity of sulfatide-containing 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) small unilamellar vesicles were examined by light scattering and the release of entrapped calcein. At 30 mol% sulfatide, stable DOPE/sulfatide vesicles were formed at the physiological pH and their stability was preserved in the presence of human plasma. These vesicles were found to be pH-sensitive and became leaky at pH 6.0 or when there was a pH-gradient across the membrane bilayer. Under such conditions, the amount of calcein released after 24 h incubation at 37 degrees C was increased by one-fold compared to that found at pH 7.4. Our results suggest that the hydration and partial dehydration of the headgroup of sulfatide upon changing pH play an essential role in determining the pH sensitivity of DOPE/sulfatide vesicles, while the importance of the condensing effect of the glycolipid on membrane bilayer is less significant.