Characteristics of the binding of Nisopropyl-p-125Iiodoamphetamine in the rat brain synaptosomal membranes

N-isopropyl-p-[125I]iodoamphetamine (125I-IMP) binding to crude synaptosomal membranes of rat brain was saturable and pharmacologically displacable. Scatchard analysis of binding data revealed an apparent dissociation constant, KDof 56.2±5.2 $mUM, and the estimated maximum number of binding sites, Bmaxof 7.5±1.1 nmoles mg-1protein; and competition studies demonstrated structure activity relationships among structural analogues of arylalkylamines. These findings suggest that the retention mechanism of IMP in the brain is probably associated with saturable binding of IMP to extreme high-density, relatively low-affinity binding sites rather than any of the well-known amine receptors.