Thermally gated liposomes: a closer look.

A homologous series of pore-forming amphiphiles (PFAs), derived from cholic acid, lysine, and spermine, have been used as "thermal gates" for releasing sucrose from liposomes made from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) [DPPG]. Binding measurements have established that these PFAs are fully bound to these liposomes in their gel state and that their transfer to fluid phase membranes is negligible. Release experiments have shown that thermal gating is sensitive to both the size and the concentration of the PFA that are used. Increases in the extent of release of sucrose with increasing temperature that have been found in the gel/fluid coexistence region indicate the existence of heterogeneity among the liposomes.