The antagonistic properties of DAU 6285, an azabicycloalkyl benzimidazolone derivative, at putative 5-hydroxytryptamine4 (5-HT4) receptors were investigated in in vitro preparations of guinea-pig ileum and human atrium, in comparison to ICS 205-930. DAU 6285 behaved as a competitive antagonist in all the preparations examined. Its affinity (pA2) ranged between 6.50 and 7.12 in the test models considered. The affinity of ICS 205-930 was 2-3 fold lower. At variance with ICS 205-930, DAU 6285 displayed a weak affinity for 5-HT3 receptors (pKi = 6.1, rat cortex; pA2 less than 5, guinea-pig ileum). In the guinea-pig ileum, DAU 6285 (10 microM) did not exert antimuscarinic, antihistaminic, antinicotinic or myolytic activity. Moreover, it did not bind to other 5-HT receptor subtypes, or to adrenergic, dopaminergic, benzodiazepine, nicotine, GABA receptors. DAU 6285 may represent a suitable tool for studies in the field of 5-HT4 receptors.
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