Takashi Yoshikawa, Naoyuki Yoshida, Yukiko Mine and Kanoo Hosoki
Discovery Research Laboratories I, Dainippon Pharmaceutical Co., Ltd.,
33-94 Enoki-cho, Suita, Osaka 564-0053, Japan
Abstract: We examined the binding affinity of mosapride citrate
(mosapride) (4-amino-5-chloro-2-ethoxy-N-{[4-(4-fluorobenzyl)-2-morpholinyl]methyl}benzamide
citrate), a novel gastroprokinetic agent, for the 5-hydroxytryptamine (5-HT)
4 receptors in guinea pig ileum using a selective 5-HT4-receptor
radioligand, [3H]GR113808. In membrane preparations from longitudinal
muscle with myenteric plexus in guinea pig ileum, specific [3H]GR113808
binding revealed a single saturable site of high affinity (Kd=0.28+/-0.02
nM, Bmax=45+/-3 fmol/mg protein). Mosapride and other 5-HT4-receptor
agonists inhibited the specific binding of [3H]GR113808 in guinea
pig ileum. The 5-HT4 agonists examined displayed the following
inhibition potency order: BIMU-8 > cisapride > mosapride > renzapride
> 5-HT > zacopride > metoclopramide. Mosapride exhibited monophasic
inhibition of the specific [3H]GR113808 binding in the ileum
(Ki value: 84.2 nM). The presence of mosapride (30 nM) significantly
increased the Kd value to 0.44+/-0.05 nM in the Scatchard analysis
of [3H]GR113808 binding. Bmax of [3H]GR113808,
however, was not affected (48+/-4 fmol/mg protein) by mosapride. As for
the affinity of mosapride, the addition of GppNHp (100 microM) slightly
increased the Ki value to 104 nM. These results indicate that
mosapride has an affinity for 5-HT4 receptors in guinea pig ileum
in the radioligand binding study.
Keywords: Mosapride citrate, 5-Hydroxytryptamine (5-HT) 4 receptor, Gastrointestinal
tract, Gastroprokinetic agent, Radioligand binding