Interaction of the local anaesthetic heptacaine with dipalmitoylphosphatidylcholine liposomes: A densimetric study

Interaction of the local anaesthetic heptacaine, monohydrochloride of [2-(h eptyloxy)-phenyl]-2-(1-piperidinyl)-ethyl ester of carbamic acid, with mult ilamellar dipalmitoylphosphatidylcholine (DPPC) liposomes in aqueous soluti on with high excess of water has been studied by means of density measureme nts in the scanning regime in the main phase transition region. The anaesth etic decreased the temperature of main phase transition. The molar partitio n coefficients of heptacaine between aqueous phase, liquid crystal and gel phases of DPPC have been determined from a combination of phase transition data obtained by densimetry with a DPPC/heptacaine phase diagram published in the literature. The saturation of heptacaine concentration in liposomes has been observed at higher total amount of anaesthetic. The partial specif ic volume of heptacaine located in DPPC bilayers is slightly lower than in the aqueous phase. (C) 1999 Elsevier Science B.V. All rights reserved.