title: An aqueous extract of Poncirus fructus activates the prokinetic activity of 5-HT receptor subtype 4 without hERG interaction.
abstract: OBJECTIVE
  Poncirus fructus (PF)--also known as the dried, immature fruit of Poncirus trifoliata (L.) Raf. (Rutaceae)--is a natural substance that has long been used for various gastrointestinal disorders in eastern Asia. An aqueous extract of PF (PF-W) has particularly potent gastroprokinetic effects, but its molecular mechanism was not well understood. Identification of the underlying prokinetic mechanism of PF-W was pursued in the present study.
  
  
  METHODS
  Changes in in vitro cAMP levels and in vivo intestinal transit rate (ITR) caused by PF-W were measured after pretreatment with GR125487, an antagonist for serotonin receptor subtype 4 (5-HT4R). An [(3)H] astemizole binding assay and electrophysiology experiments were performed to determine if PF-W has any interaction with the human ether-à-go-go related gene (hERG) potassium channel.
  
  
  RESULTS
  PF-W induced an increase in intracellular cAMP in 5-HT4R-expressing HEK293T cells, indicating that PF-W does activate 5-HT4R. Moreover, pretreatment with GR125487 successfully blocked the increase, suggesting that the response was 5-HT4R-specific. More importantly, pretreatment of GR125487 in rats inhibited the elevation of ITR by PF-W, indicating that the prokinetic effect of PF-W was indeed exerted via 5-HT4R. On the other hand, both [(3)H]-astemizole binding assay and electrophysiological experiments revealed that PF-W did not interfere at all with the hERG channel.
  
  
  CONCLUSIONS
  It was found that PF-W exerts its prokinetic activity through a 5-HT4R-mediated pathway, with no interaction with hERG channels. Therefore, PF-W is a good candidate that might be developed as a prokinetic agent with fewer expected cardiac side effects.
authors.affiliation: National Research Laboratory for Transporters Targeted Drug Design & Research Institute of Pharmaceutical Sciences and Department of Pharmaceutics, College of Pharmacy, Seoul National University, 599 Gwanangno, Gwanak-gu, Seoul 151-742, Republic of Korea.
authors.forename: Won-Sik
authors.initials: WS
authors.lastname: Shim
authors.forename: Heejung
authors.initials: H
authors.lastname: Back
authors.forename: Sang-Won
authors.initials: SW
authors.lastname: Jung
authors.forename: Jun-Woo
authors.initials: JW
authors.lastname: Kim
authors.forename: Yongwoo
authors.initials: Y
authors.lastname: Jang
authors.forename: Byeongjun
authors.initials: B
authors.lastname: Lee
authors.forename: Eun-Kyoung
authors.initials: EK
authors.lastname: Seo
authors.forename: Uhtaek
authors.initials: U
authors.lastname: Oh
authors.forename: Chang-Koo
authors.initials: CK
authors.lastname: Shim
mesh_terms: D000818:Animals; D016589:Astemizole / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics / Q000378:metabolism*; D005638:Fruit / Q000737:chemistry; D005772:Gastrointestinal Transit / Q000187:drug effects*; D006801:Humans; D018408:Patch-Clamp Techniques; D010936:Plant Extracts / Q000009:adverse effects / Q000302:isolation & purification / Q000494:pharmacology*; D032104:Poncirus / Q000737:chemistry*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D044422:Receptors, Serotonin, 5-HT4 / Q000235:genetics / Q000378:metabolism*; D058828:Serotonin 5-HT4 Receptor Agonists / Q000009:adverse effects / Q000302:isolation & purification / Q000494:pharmacology*; D058832:Serotonin 5-HT4 Receptor Antagonists / Q000494:pharmacology; D014162:Transfection
chemical_list: D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D010936:Plant Extracts; D026902:Potassium Channel Blockers; D058828:Serotonin 5-HT4 Receptor Agonists; D058832:Serotonin 5-HT4 Receptor Antagonists; D044422:Receptors, Serotonin, 5-HT4; D016589:Astemizole; D000242:Cyclic AMP