title: Hyperpolarization-activated cyclic nucleotide-gated cation channel subtypes differentially modulate the excitability of murine small intestinal afferents.
abstract: OBJECTIVE
  To assess the role of hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels in regulating the excitability of vagal and spinal gut afferents.
  
  
  METHODS
  The mechanosensory response of mesenteric afferent activity was measured in an ex vivo murine jejunum preparation. HCN channel activity was recorded through voltage and current clamp in acutely dissociated dorsal root ganglia (DRG) and nodose ganglia (NG) neurons retrogradely labeled from the small intestine through injection of a fluorescent marker (DiI). The isoforms of HCN channels expressed in DRG and NG neurons were examined by immunohistochemistry.
  
  
  RESULTS
  Ramp distension of the small intestine evoked biphasic increases in the afferent nerve activity, reflecting the activation of low- and high-threshold fibers. HCN blocker CsCl (5 mmol/L) preferentially inhibited the responses of low-threshold fibers to distension and showed no significant effects on the high-threshold responses. The effect of CsCl was mimicked by the more selective HCN blocker ZD7288 (10 μmol/L). In 71.4% of DiI labeled DRG neurons (n = 20) and 90.9% of DiI labeled NG neurons (n = 10), an inward current (I(h) current) was evoked by hyperpolarization pulses which was fully eliminated by extracellular CsCl. In neurons expressing I(h) current, a typical "sag" was observed upon injection of hyperpolarizing current pulses in current-clamp recordings. CsCl abolished the sag entirely. In some DiI labeled DRG neurons, the I(h) current was potentiated by 8-Br-cAMP, which had no effect on the I(h) current of DiI labeled NG neurons. Immunohistochemistry revealed differential expression of HCN isoforms in vagal and spinal afferents, and HCN(2) and HCN(3) seemed to be the dominant isoform in DRG and NG, respectively.
  
  
  CONCLUSIONS
  HCNs differentially regulate the excitability of vagal and spinal afferent of murine small intestine.
authors.affiliation: Department of Physiology, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China.
authors.forename: Ying-Ping
authors.initials: YP
authors.lastname: Wang
authors.forename: Bi-Ying
authors.initials: BY
authors.lastname: Sun
authors.forename: Qian
authors.initials: Q
authors.lastname: Li
authors.forename: Li
authors.initials: L
authors.lastname: Dong
authors.forename: Guo-Hua
authors.initials: GH
authors.lastname: Zhang
authors.forename: David
authors.initials: D
authors.lastname: Grundy
authors.forename: Wei-Fang
authors.initials: WF
authors.lastname: Rong
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000378:metabolism; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002478:Cells, Cultured; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000166:cytology; D007421:Intestine, Small / Q000294:innervation*; D008297:Male; D008465:Mechanoreceptors / Q000166:cytology / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D009475:Neurons, Afferent / Q000166:cytology / Q000378:metabolism*; D009620:Nodose Ganglion / Q000166:cytology; D018408:Patch-Clamp Techniques; D011312:Pressure; D020033:Protein Isoforms / Q000378:metabolism*
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels; D020033:Protein Isoforms; D015124:8-Bromo Cyclic Adenosine Monophosphate