Interactions of phenytoin with rat brain synaptosomes examined by fluorescent fatty acid probes

Phenytoin (PHT) modified the fluorescent characteristics of anthroyloxy-fatty acids in synaptosomal membranes. Association of PHT with synaptosomal membranes caused the greatest change when the fluorescent probe was located at the 6-carbon position of N-(anthroyloxy)stearic acid and was incorporated into the membranes. Phenytoin and 6-(anthroyloxy)stearic acid compete for high affinity binding regions which are probably lipid domains within the membrane. Phenytoin has a weaker association with the sites than the fluorescent fatty acids. Divalent cations, e.g. Mg(2+) or Ca(2+), are required to observe maximal change in polarization of fluorescence of fatty acid probes in the presence of PHT. It is proposed that the membrane lipid bilayer reorganizes to accommodate exogenous compounds, such as phenytoin or the fatty acid probe in order to permit the most efficient packing of lipids. This reorganization of the lipid bilayer may influence membrane enzyme activities and ion channels.