Ketanserin and ritanserin discriminate between recombinant human 5-HT sub(1D alpha ) and 5-HT sub(1D beta ) receptor subtypes

Compounds able to discriminate functionally between the closely related cloned human 5-HT sub(1D alpha ) and 5-HT sub(1D beta ) receptor subtypes have not been reported previously. In [ super(3)H]5-HT competition assays, the classical 5-HT sub(2A) receptor antagonists, ritanserin and ketanserin, displayed moderate affinity (pK sub(i) = 7.30 and 7.17, respectively) and marked selectivity (22-and 71-fold, respectively) for the recombinant human 5-HT sub(1D alpha ) subtype relative to the 5-HT sub(1D beta ) receptor. In contrast, the nonselective 5-HT sub( one half ) receptor antagonist, methiothepin, exhibited similar binding affinities (pK sub(i) = 7.64-8.01) for both recombinant 5-HT sub(1D) subtypes. The antagonistic properties of these compounds were evaluated for their ability to block 5-HT-induced inhibition of forskolin-stimulated cAMP accumulation in intact cells stably expressing either 5-HT sub(1D alpha ) or 5-HT sub(1D beta ) receptors. All three compounds behaved as antagonists devoid of intrinsic activity in the functional assays. The apparent pK sub(b) values determined in functional assays closely matched their pK sub(i) values obtained in binding assays. Since ketanserin exhibits significant selectivity for the human 5-HT sub(1D alpha ) receptor, this antagonist can be used as a pharmacological tool to discriminate between 5-HT sub(1D alpha ) and 5-HT sub(1D beta ) receptor-mediated responses in human tissues.