The antagonism effect of sertindole on alpha 1-AR subtypes was studied by combining radiologand binding assays in three cloned alpha 1-AR subtypes stably expressed in human embryonic kidney 293 cells and contractile response experiment in isolated rat blood vessels. The results showed that the affinity for sertindole in the cloned alpha 1A-AR (pKI 8.90 +/- 0.17) was 69-fold (pKI 7.06 +/- 0.09) and 132-fold (pKI 6.78 +/- 0.07) higher than that for the cloned alpha 1B- and alpha 1D-AR, respectively. The pA2 values for sertindole in antagonizing NE-induced vasoconstriction in isolated rat aorta and renal artery were shown to fit well to the pKI values on cloned alpha 1D- and alpha 1A-AR, respectively. Pretreatment of membrane preparations with sertindole for 30 min significantly reduced the maximal binding capacities. (Bmax) of 125 IBE2254 to the three cloned alpha 1-AR subtypes without alteration of affinities (KD values). In the presence of sertindole, the Bmax of 125IBE2254 binding to the cloned alpha 1-ARs were not significantly changed, while the KD values were significantly increased. Thus, sertindole is a selective irreversible competitive alpha 1-AR antagonist with alpha 1A subtype.