Regulation of the 5-HT₃A receptor-mediated current by alkyl 4-hydroxybenzoates isolated from the seeds of Nelumbo nucifera

Four known alkyl 4-hydroxybenzoates, i.e., methyl 4-hydroxybenzoate (1), ethyl 4-hydroxybenzoate (2), propyl 4-hydroxybenzoate (3), and butyl 4-hydroxybenzoate (4), were isolated from the seeds of Nelumbo nucifera GAERTNER (Nymphaeaceae) for the first time. The structures of the isolates were identified by 1D- and 2D-NMR spectroscopy and comparison with published values. The compounds were evaluated for their effects on the 5-HT-stimulated inward current (I_5-HT) mediated by the human 5-HT₃A receptors expressed in Xenopus oocytes. Compounds 1 and 2 enhanced the I_5-HT, but 4 reduced it. These results indicate that 4 is an inhibitor of the 5-HT ₃A receptors expressed in Xenopus oocytes.