High affinity binding of [ 3H]paroxetine and [ 3H]imipramine to human platelet membranes

Paroxetine, one of the most potent and specific serotonin uptake inhibitors, was tritiated and used for binding studies with human platelet membranes. Specific, high affinity binding was demonstrated. The binding was compared with [ 3H]imipramine binding; it was found that the maximal binding (B max) was the same for [ 3H]paroxetine and [ 3H]imipramine, whereas the affinity was much higher for [ 3H]paroxetine (K D 0.08 nM and 0.56 nM for paroxetine and imipramine binding, respectively). IC 50 was calculated for the inhibition of [ 3H]paroxetine and [ 3H]imipramine binding by a number of antidepressants; the corresponding Hill coefficients were also calculated.