INTERACTION OF CHLORPROMAZINE WITH PHOSPHOLIPID-MEMBRANES - AN EPR STUDY OF MEMBRANE-SURFACE POTENTIAL EFFECTS

The interaction of chlorpromazine (CPZ) with artificial membranes (egg -yolk phosphatidylcholine liposomes) has been studied. Measurements of the surface electric potential, which is modified in the presence of the ionized form of the drug, were obtained by electron paramagnetic r esonance spectroscopy (EPR) using a positively charged amphiphilic spi n-probe. This probe partitions between the aqueous and lipidic phases depending on the sur face potential and on the structural state of the membrane. The surface potential was measured as a function of drug co ncentration in the range where the spectral line-shapes are not affect ed by the incorporation of the drug. From these experimental results a nd through an appropriate formalism we obtain information on the bindi ng of the drug to the lipid bilayer and on the ionization of the drug in the lipidic phase.