title: Involvement of Transient Receptor Potential Vanilloid Receptor 1, (TRPV1)-Expressing Vagal Nerve in the Inhibitory Effect of Gastric Acidification on Exogenous Motilin-Induced Gastric Phase III Contractions in Suncus murinus.
abstract: Gastric acidification inhibits motilin-induced gastric phase III contractions. However, the underlying mechanism has not been thoroughly investigated. Here, we studied the inhibitory mechanism by gastric acidification on motilin-induced contraction in Suncus murinus (S. murinus).
  
  
  
  We measured interdigestive gastric phase III contractions in conscious, freely moving S. murinus, and examined the inhibitory effect of gastric acidification on motilin action and the involvement of the vagus nerve and transient receptor potential vanilloid receptor 1 (TRPV1) in the inhibitory mechanism.
  
  
  
  A bolus injection of motilin evoked phase III-like contractions during intravenous infusion of saline. Intragastric acidification (pH 1.5-2.5) inhibited motilin-induced phase III contractions in a pH-dependent manner and significantly decreased the motility index at a pH below 2.0. In contrast, intraduodenal acidification (pH 2.0) failed to inhibit motilin-induced contractions. Vagotomy significantly alleviated the suppression of motilin-induced gastric contractions under acidic conditions (pH 2.0), suggesting vagus nerve involvement. Moreover, intragastric acidification (pH 2.0) significantly increased the number of c-Fos-positive cells in the nucleus tractus solitarii. In vagotomized S. murinus, the number of c-Fos-positive cells did not change, even under gastric acidification conditions. TRPV1 mRNA was highly expressed in the muscle and mucosal regions of the antrum and the nodose ganglion, whereas was not detected in the upper small intestine. Capsazepin, a TRPV1 antagonist, completely rescued the inhibitory effect of gastric acidification.
  
  
  
  Gastric acidification in S. murinus inhibits motilin-induced contractions, a finding similar to results observed in humans, while TRPV1-expressing vagus nerves play a role in the inhibitory mechanism.
authors: Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors: Makoto
authors: M
authors: Yoshimura
authors: Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors: Takashi
authors: T
authors: Mikami
authors: Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors: Kayuri
authors: K
authors: Kuroda
authors: Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors: Maki
authors: M
authors: Nishida
authors: Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors: Kazuma
authors: K
authors: Ito
authors: Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors: Anupom
authors: A
authors: Mondal
authors: Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors: Kouhei
authors: K
authors: Koyama
authors: Laboratory of Animal Management and Resources, Department of Zoology, Faculty of Science, Okayama University of Science, Okayama, 700-8525, Japan.
authors: Takamichi
authors: T
authors: Jogahara
authors: Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors: Ichiro
authors: I
authors: Sakata
authors: Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan. tsakai@mail.saitama-u.ac.jp.
authors: Takafumi
authors: T
authors: Sakai
mesh_terms: D000818:Animals; D005260:Female; D005769:Gastrointestinal Motility / Q000187:drug effects*; D008297:Male; D009037:Motilin / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D012788:Shrews; D013270:Stomach / Q000502:physiology*; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism*; D014630:Vagus Nerve / Q000378:metabolism*
chemical_list: D050916:TRPV Cation Channels; D009037:Motilin
keywords: Gastric acidification; Motilin; Phase III contraction; TRPV1; Vagus nerve