bimu 8 is an agonist of 5-ht4 with ki values of 33.9 ± 8.0 nm and 12.6 ± 0.9 nm in guinea pig ileum and striatum, respectively [1, 2].as a member of the seven transmembrane spanning g-protein-coupled family of receptors, the 5-ht4 receptor is positively coupled to adenylate cyclase. it exists in two isoforms (5-ht4s and 5-ht4l). these two isoforms differ in the sequence and length of their carboxy termini [3].bimu 8 significantly decreased the k+ current in colliculi neurons. this suggested a 5-ht4 receptor-mediated effect [4]. in neurons, bimu 8 at concentrations ranging from 0.003-0.1 μm increased epsp amplitude but did not change membrane potential. the epsp potentiation induced by bimu 8 was blocked by tropisetron (1 μm), a 5-ht3/5-ht4 receptor antagonist. but ondansetron (1 μm), a 5-ht3 receptor antagonist did not blocked the epsp potentiation induced by bimu 8 [5].in the hot-plate test, bimu 8 injected i.p. in the range of doses of 20-30 mg/kg significantly induced an increase in the pain threshold. 15 min after administration, the antinociceptive effect reached a maximum and hence diminished. this effect disappeared within 45 min. choline uptake blocker hc-3 (1 μg per mouse i.c.v.), antimuscarinic drug atropine (5 mg/kg i.p.), 5-ht4 antagonists sdz 205-557 (10 mg/kg i.p.) and gr 125487 (20 mg/kg i.p.) completely prevented the antinociception of bimu 8 [1].
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[4]. fagni l, dumuis a, sebben m, et al. the 5-ht4 receptor subtype inhibits k+ current in colliculi neurones via activation of a cyclic amp-dependent protein kinase. british journal of pharmacology, 1992, 105(4): 973-979.
[5]. pan h, galligan jj. 5-ht1a and 5-ht4 receptors mediate inhibition and facilitation of fast synaptic transmission in enteric neurons. american journal of physiology-gastrointestinal and liver physiology, 1994, 266(2): g230-g238.
