title: Altered purinergic signaling in colorectal dorsal root ganglion neurons contributes to colorectal hypersensitivity.
abstract: Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by pain and hypersensitivity in the relative absence of colon inflammation or structural changes. To assess the role of P2X receptors expressed in colorectal dorsal root ganglion (c-DRG) neurons and colon hypersensitivity, we studied excitability and purinergic signaling of retrogradely labeled mouse thoracolumbar (TL) and lumbosacral (LS) c-DRG neurons after intracolonic treatment with saline or zymosan (which reproduces 2 major features of IBS-persistent colorectal hypersensitivity without inflammation) using patch-clamp, immunohistochemical, and RT-PCR techniques. Although whole cell capacitances did not differ between LS and TL c-DRG neurons and were not changed after zymosan treatment, membrane excitability was increased in LS and TL c-DRG neurons from zymosan-treated mice. Purinergic agonist adenosine-5'-triphosphate (ATP) and α,β-methylene ATP [α,β-meATP] produced inward currents in TL c-DRG neurons were predominantly P2X(3)-like fast (∼70% of responsive neurons); P2X(2/3)-like slow currents were more common in LS c-DRG neurons (∼35% of responsive neurons). Transient currents were not produced by either agonist in c-DRG neurons from P2X(3)(-/-) mice. Neither total whole cell Kv current density nor the sustained or transient Kv components was changed in c-DRG neurons after zymosan treatment. The number of cells expressing P2X(3) protein and its mRNA and the kinetic properties of ATP- and α,β-meATP-evoked currents in c-DRG neurons were not changed by zymosan treatment. However, the EC(50) of α,β-meATP for the fast current decreased significantly in TL c-DRG neurons. These findings suggest that colorectal hypersensitivity produced by intracolonic zymosan increases excitability and enhances purinergic signaling in c-DRG neurons.
authors.affiliation: Center for Pain Research, Department of Anesthesiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA. shinoda-m@dent.nihon-u.ac.jp
authors.forename: Masamichi
authors.initials: M
authors.lastname: Shinoda
authors.forename: Jun-Ho
authors.initials: JH
authors.lastname: La
authors.forename: Klaus
authors.initials: K
authors.lastname: Bielefeldt
authors.forename: G F
authors.initials: GF
authors.lastname: Gebhart
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D003106:Colon / Q000294:innervation* / Q000503:physiopathology; D004305:Dose-Response Relationship, Drug; D005727:Ganglia, Spinal / Q000503:physiopathology*; D043183:Irritable Bowel Syndrome / Q000503:physiopathology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D058911:Purinergic P2X Receptor Agonists / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D058477:Receptors, Purinergic P2X3 / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D012007:Rectum / Q000294:innervation* / Q000503:physiopathology; D011984:Sensory Receptor Cells / Q000502:physiology*; D013153:Splanchnic Nerves / Q000503:physiopathology*; D015054:Zymosan / Q000633:toxicity
chemical_list: D058911:Purinergic P2X Receptor Agonists; D012333:RNA, Messenger; D058477:Receptors, Purinergic P2X3; D000255:Adenosine Triphosphate; D015054:Zymosan; C002630:alpha,beta-methyleneadenosine 5'-triphosphate