Signalling pathways responsible for the methylisogermabullone-induced contraction of ileal longitudinal muscles

Objectives We have previously reported that methylisogermabullone (MIGB) stimulates small bowel motility through activation of acetylcholinergic receptors. This study investigated the cellular signalling pathways implicated in the regulation of ileal contractility by MIGB. Methods The ileal longitudinal muscles prepared from rats were treated with MIGB isolated from radish roots, and muscle contractility and protein expression were measured by force transducer and Western blot, respectively. Key findings MIGB at 30 Âμm induced a sustained phasic contraction of ileal longitudinal muscles. Acetylcholine (ACh, 0.5 Âμm) and MIGB stimulated translocation of protein kinase C (PKC) to cell membrane of ileal longitudinal muscles, and these stimulatory effects were remarkably attenuated by atropine (0.5 Âμm). ACh and MIGB induced phosphorylation of ERK 1/2 and p38 MAPKs in ileal longitudinal muscles, and they also phosphorylated the caldesmon and 20-kDa regulatory light chain of myosin (MLC₂₀). Additionally, PD-98058 (10 Âμm), a selective ERK 1/2 MAPK inhibitor, and SB-203580 (10 Âμm), a selective p38 MAPK inhibitor, significantly reduced the MIGB-induced contraction of ileal longitudinal muscles. Conclusions The muscarinic receptor activated by MIGB translocates the PKC to cell membrane which phosphorylates the ERK 1/2 and p38 MAPKs, resulting in subsequent phosphorylation of caldesmon and MLC₂₀. These cellular events likely converge on the contraction of ileal longitudinal muscles in rats.