STABILITY AND PH SENSITIVITY OF SULFATIDE-CONTAINING PHOSPHATIDYLETHANOLAMINE SMALL UNILAMELLAR VESICLES

The bilayer stabilization effect of sulfatide and the pH sensitivity o f 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/s ulfatide vesicles were formed at the physiological pH and their stabil ity 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 then 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 i ncreased by one fold compared to that found at pH 7.4. Our results sug gest that the hydration and partial dehydration of the headgroup of su lfatide upon changing pH play an essential role in determining the pH sensitivity of DOPE/sulfatide vesicles, while the importance of the co ndensing effect of the glycolipid on membrane bilayer is less signific ant.