Subcellular distribution of high affinity [³H]imipramine binding and [³H]serotonin uptake in rat brain

The binding of [³H]imipramine to various subcellular fractions of rat brain was investigated. Using sodium free buffer or 0.5 μM chlorimipramine to define nonspecific binding, the specific binding was found to be associated with the synaptosomal fraction, as was the uptake of [³H]serotonin. A significant quantity of 'displaceable' binding was observed in the myelin and nuclear fractions when 'specific' binding was defined using only one concentration of [³H]imipramine and a large molar excess of chlorimipramine. This 'pseudospecific' binding was of low affinity and was not affected by the presence or absence of sodium.