The Interaction of Phenothiazine Derivatives with Synaptosomal Membranes: the Use of Fluorescent Probes as an Indicator of Drug-Induced Conformational Perturbations

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Abstract
The effects of two phenothiazine derivatives, chlorpromazine and chlorpromazine sulfoxide, were studied on synaptic membranes derived from rat cerebral cortex. The fluorescent probe 1 -anilino-8-naphthalene sulfonate (ANS) was used to determine whether these drugs were capable of altering membrane structure. The results of this study indicate that the probe is bound to the membrane resulting in an enhanced fluorescence of the ANS and a blue spectral shaft of some 43 nm in its emission spectrum. Titration of the ANS-membrane complex in the presence of 1 × 10−4 M chlorpromazine indicated that the drug alters the membrane structure in such a way as to create additional ANS binding sites. This finding was verified by the use of double-reciprocal plots of protein versus fluorescence in the presence and absence of the drug. When chlorpromazine sulfoxide was used as the neuro-perturbant the same general effect was noted but to a much smaller degree. These findings substantiate theories regarding the mechanism of action of these drugs and show that not only do psychoactive agents have the ability to alter neuronal membrane structure but that the fluorescent probe technique may prove to be useful in studying such events in isolated in vitro preparations at the molecular level.