EFFECT OF MEMBRANE-SURFACE POTENTIAL ON THE UPTAKE OF ANIONIC COMPOUNDS BY LIPOSOMES

The effect of membrane surface potential on the uptake of several anio nic compounds by liposomes (large unilamellar vesicles), which contain various amounts of dipalmitoylphosphatidylserine (DPPS), was investig ated. The uptake amount of four tested anionic compounds (cefixime, be nzyioxyindoleacetic acid (BOIAA), ceftibuten and S-1006) decreased wit h an increase in the DPPS content of liposomes, and was correlated wit h the membrane surface potential monitored using a fluorescent dye, 8- anilino-1-naphthalene sulfonate (ANS). Moreover, for all of the tested anionic compounds, a good correlation was observed between the ratio of the uptake value (5 min) by each of the liposomes comprising variou s amounts of DPPS to the uptake value by liposomes containing 10% DPPS and a relative membrane surface potential monitored by ANS. On the ot her hand, the uptake of zwitterionic compounds (enoxacin, cephradine a nd benzyloxytryptophan (BOTP)) was independent of DPPS content. These results suggest that the uptake of tested anionic compounds by large u nilamellar lipid vesicles is dependent on the membrane surface potenti al which originates in the surface negative charge.