In vitro effects of psychotropic agents on the microviscosity of platelet membranes.

Normal platelet membranes were exposed in vitro to a variety of psychotropic agents, including chlorpromazine, fluphenazine, haloperidol, imipramine, and lithium. Changes in microviscosity of the hydrocarbon layer of the drug-exposed membranes were determined by steady-state fluorescence polarization measurements, employing the fluorescent probe 1,6-diphenyl 1,3,5-hexatriene (DPH). Concentrations of the phenothiazines chlorpromazine and fluphenazine above 200 nM produced significant increases in microviscosity, while haloperidol produced a small but consistent decrease in microviscosity in the concentration range of 200 nM to 200 microM. Imipramine and lithium were without effect. The phenothiazine-induced increase in microviscosity was apparently dependent upon the structure of the phenothiazine nucleus; side chain structure was less important to this effect.