Characterization of [

Coated vesicles prepared from bovine brain cerebral cortex exhibited [

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]5-hydroxytryptamine (5-HT, serotonin) and [

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]spiperone binding activities. The binding activities were localized in the inner core vesicles. Binding reached an equilibrium level by 30–45 min at 30°C, and was reversed by the addition of 100 μM 5-HT for [

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]5-HT binding or 10 μM ketanserin for [

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]spiperone binding. The saturation binding experiments indicated a single class of binding sites for [

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]5-HT and [

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]spiperone with apparent K_d values of 2.4 and 1.75 nM, respectively. The binding of [

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]5-HT was displaced by 5-HT and 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), but not by ketanserin. The binding of [

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]spiperone was displaced by spiperone and ketanserin but not by 5-HT or 8-OH-DPAT even at 1 mM. The coated vesicles were shown by immunoblotting assay to contain α-subunits of GTP-binding proteins, Gαs, Gαi2, Gαi3, Gαo and Gαq/11. Forskolin-stimulated adenylate cyclase activity in the coated vesicles was inhibited to 80% of the control level by 5-HT or 8-OH-DPAT. These results suggested that 5-HT_1A and 5-HT_2A receptors are present in bovine brain coated vesicles and that the 5-HT_1A receptors are coupled to adenylate cyclase activity via GTP binding proteins.