Interaction of Diphenylhydantoin-4-14C with Subcellular Fractions of Rat Brain

Abstract

The mode and site of action of diphenylhydantoin (DPH) in the brain are unknown. We studied the binding of DPH to subcellular fractions of the brain of male Wistar rats, which previously had been injected with DPH-4-¹⁴C and killed at intervals. At most times the distribution of the radioactivity among the fractions was similar to that observed when the drug was added after homogenization. However, 12 h after injection there was increased concentration in a heavy microsomal fraction which contains mainly small nerve endings. Measurement of radioactivity in submitochondrial fractions indicated that redistribution was occurring during fractionation. Subcellular fractions from brains of uninjected rats were dialyzed against solutions containing DPH-4-¹⁴C and various electrolytes. DPH tends to bind to fractions containing plasma membranes. The degree of binding was decreased by the presence of Ca²⁺ in the dialysis solution while Mg²⁺ had no effect. When both ions were present at concentrations of 12.1 mM Mg²⁺ and 1.4 mM Ca²⁺, binding was the same as when ions were not present. The data suggest that DPH interacts with plasma membranes by electrostatic forces and that this interaction is altered by Ca²⁺.