FUSION BETWEEN RAT-BRAIN SYNAPTOSOMES AND PHOSPHATIDYLSERINE LIPOSOMES

Synaptosomal fractions isolated from rat cerebral cortex were incubated in the absence and presence of phosphatidylserine (PS) liposomes. The PS treated synaptosomes yielded lighter bouyant bands when centrifugated on discontinuous sucrose gradients. In these bands an increase in the lipidic phosphorus/protein ratio together with a massive incorporation of PS and a relative decrease of phosphatidylcholine was observed. Besides, in the synaptosomes treated with PS (0.5-0.7-mu-g/mg protein). Na+, K+-ATPase activity was 30-50% higher than in the controls. We have employed an assay for lipid mixing based on the self-quenching relief of octadecylrhodamine B fluorescence. The decrease in the self-quenching of the probe in the gradient bands of liposomes treated synaptosomes, besides the chemical analysis data, indicated that a fusion process between synaptosomes and liposomes has taken place. It is the first time that a fusion process is proved between native synaptosomes and an artificial lipidic membrane.