title: Neural FFA3 activation inversely regulates anion secretion evoked by nicotinic ACh receptor activation in rat proximal colon.
abstract: Luminal short-chain fatty acids (SCFAs) influence gut physiological function via SCFA receptors and transporters. The contribution of an SCFA receptor, free fatty acid receptor (FFA)3, to the enteric nervous system is unknown. FFA3 is expressed in enteric cholinergic neurons. Activation of neural FFA3 suppresses Cl(-) secretion induced by nicotinic ACh receptor activation via a Gi/o pathway. Neural FFA3 may have an anti-secretory function by modulating cholinergic neural reflexes in the enteric nervous system.
  
  
  
  The proximal colonic mucosa is constantly exposed to high concentrations of microbially-produced short-chain fatty acids (SCFAs). Although luminal SCFAs evoke electrogenic anion secretion and smooth muscle contractility via neural and non-neural cholinergic pathways in the colon, the involvement of the SCFA receptor free fatty acid receptor (FFA)3, one of the free fatty acid receptor family members, has not been clarified. We investigated the contribution of FFA3 to cholinergic-mediated secretory responses in rat proximal colon. FFA3 was immunolocalized to enteroendocrine cells and to the enteric neural plexuses. Most FFA3-immunoreactive nerve fibres and nerve endings were cholinergic, colocalized with protein gene product (PGP)9.5, the vesicular ACh transporter, and the high-affinity choline transporter CHT1. In Ussing chambered mucosa-submucosa preparations (including the submucosal plexus) of rat proximal colon, carbachol (CCh)-induced Cl(-) secretion was decreased by TTX, hexamethonium, and the serosal FFA3 agonists acetate or propionate, although not by an inactive analogue 3-chloropropionate. Serosal application of a selective FFA3 agonist (N-[2-methylphenyl]-[4-furan-3-yl]-2-methyl-5-oxo-1,4,5,6,7,8-hexahydro-quinoline-3-carboxamide; MQC) dose-dependently suppressed the response to CCh but not to forskolin, with an IC50 of 13 μm. Pretreatment with MQC inhibited nicotine-evoked but not bethanechol-evoked secretion. The inhibitory effect of MQC was reversed by pretreatment with pertussis toxin, indicating that FFA3 acts via the Gi/o pathway. Luminal propionate induced Cl(-) secretion via the cholinergic pathway, which was reduced by MQC, as well as by TTX, hexamethonium or removal of the submucosal plexus. These results suggest that the SCFA-FFA3 pathway has a novel anti-secretory function in that it inhibits cholinergic neural reflexes in the enteric nervous system.
authors: Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.|Brentwood Biomedical Research Institution, Los Angeles, CA, USA.
authors: Izumi
authors: I
authors: Kaji
authors: Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, CA, USA.|Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.|Brentwood Biomedical Research Institution, Los Angeles, CA, USA.
authors: Yasutada
authors: Y
authors: Akiba
authors: Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors: Kohtarou
authors: K
authors: Konno
authors: Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors: Masahiko
authors: M
authors: Watanabe
authors: Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors: Shunsuke
authors: S
authors: Kimura
authors: Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors: Toshihiko
authors: T
authors: Iwanaga
authors: University of Shizuoka Graduate School of Integrated Pharmaceutical and Nutritional Sciences, Shizuoka, Japan.
authors: Ayaka
authors: A
authors: Kuri
authors: University of Shizuoka Graduate School of Integrated Pharmaceutical and Nutritional Sciences, Shizuoka, Japan.
authors: Ken-Ichi
authors: K
authors: Iwamoto
authors: University of Shizuoka Graduate School of Integrated Pharmaceutical and Nutritional Sciences, Shizuoka, Japan.
authors: Atsukazu
authors: A
authors: Kuwahara
authors: Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, CA, USA.|Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.|Department of Surgery, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.|Brentwood Biomedical Research Institution, Los Angeles, CA, USA.
authors: Jonathan D
authors: JD
authors: Kaunitz
mesh_terms: D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism; D003106:Colon / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D017615:Enteric Nervous System / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009474:Neurons / Q000502:physiology; D011422:Propionates / Q000494:pharmacology; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism / Q000502:physiology*; D011978:Receptors, Nicotinic / Q000502:physiology
chemical_list: D002712:Chlorides; D011422:Propionates; D043562:Receptors, G-Protein-Coupled; D011978:Receptors, Nicotinic; D002217:Carbachol