NAD-299 ANTAGONISES 5-HT-STIMULATED AND SPIPERONE-INHIBITED [³⁵S]GTPγS BINDING IN CLONED 5-HT_1ARECEPTORS

In Chinese Hamster Ovary (CHO) cells expressing cloned human 5-hydroxy-tryptamine(1A) (5-HT1A) receptors, (R)-3-NN-dicyclobutylamino-8-fluoro[6-(3) H]-3,4-dihydro-2H-1-benzopyran-5-carboxamide ([H-3]NAD-299) exhibited high affinity (K-d = 0. 16 nM) and labeled 34% more receptors than 8-hydroxy2-([2,3 -(3) H]di-n-propylamino)tetralin ([H-3]8-OH-DPAT). NAD-299 behaved as a silent antagonist in [S-35]GTPgammaS binding similar to N-tert-butyl-3-(4-(2-methoxyphenyl)-piperazin-1-yl)-2-phenylpropanamide (WAY-100635) and (S)-5-fluoro-8-hydroxy-2-(di-n-propylamino)tetralin ((S)UH-301). 5-HT and 5-carboxamidotryptamine (5-CT) stimulated [S-35]GTPgammaS binding 2.5-fold while spiperone and methiothepin inhibited [S-35]GTPgammaS binding 1.4-fold. Furthermore, NAD-299 antagonised both the 5-HT stimulated and the spiperone inhibited [S-35]GTPgammaS binding to basal levels. The K-iL/K-iH ratios for spiperone (0.66), methiothepin (0.39), WAY-100635 (0.32), (S)UH-301 (0.94), NAD-299 (1.29), NAN-190 (1.23), (S)pindolol (5.85), ipsapirone (13.1), buspirone (24.6), (+/-)8-OH-DPAT (47.3), flesinoxan (55.8), 5-HT (200) and 5-CT (389) correlated highly significantly with the intrinsic activity obtained with [S-35] GTPgammaS (r = 0.97).