title: Role of calcium in activation of hyperpolarization-activated cyclic nucleotide-gated channels caused by cholecystokinin octapeptide in interstitial cells of cajal.
abstract: BACKGROUND
  Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels regulate pacemaker activity in some cardiac cells and neurons. Little is known about the effects of cholecystokinin octapeptide (CCK-8) on HCN channels and excitability of murine interstitial cells of Cajal (ICCs).
  
  
  METHODS
  In the present study, the effects and mechanisms of CCK-8 on HCN channels were investigated by measuring mechanical contraction of smooth muscle strips and ionic channels of ICCs in murine gastric antrum.
  
  
  RESULTS
  Sulfated CCK-8 (CCK-8S) was used, and we found that CCK-8S increased the contraction of smooth muscle strips in the gastric antrum, which could be suppressed by specific HCN channel blockers CsCl and ZD7288. Extracellular calcium could also intensify the contraction. Under the same conditions, when antral strips were exposed to calcium ion (Ca²⁺)-free solution, no significant changes could be recorded with CCK-8S or ZD7288. Isolated ICCs from the murine gastric antrum identified by specific c-Kit antibody primers were chosen for electrophysiological recordings. HCN current (I(h)) of cultured ICCs was studied by whole-cell patch clamp techniques. A spontaneous transient inward current was recorded in ICCs, which could be inhibited by addition of CsCl and ZD7288; the current proved to be I(h). CCK-8S-facilitated I(h) in cultured ICCs could be inhibited by CsCl and ZD7288. When cultured ICCs were exposed to Ca²⁺-free solution, no significant changes could be recorded by application of CCK-8S on I(h), which proved extracellular calcium might have an excitatory effect on HCN channels.
  
  
  CONCLUSIONS
  We demonstrate that HCN channels are present in ICCs in the murine gastric antrum; they might be an important regulator of ICC excitability and pacemaker activity and are strongly affected by CCK-8S. Extracellular calcium might be a trigger in the activation of HCN channels caused by CCK-8S in cultured ICCs.
authors.affiliation: Department of Gastroenterology, The First Affiliated Hospital of Nanjing Medical University, Guangzhou Road 300, Nanjing 210029, China. sixinmin@126.com
authors.forename: Xinmin
authors.initials: X
authors.lastname: Si
authors.forename: Lei
authors.initials: L
authors.lastname: Huang
authors.forename: Yaoyao
authors.initials: Y
authors.lastname: Gong
authors.forename: Jia
authors.initials: J
authors.lastname: Lu
authors.forename: Lin
authors.initials: L
authors.lastname: Lin
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000187:drug effects / Q000502:physiology*; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D056885:Interstitial Cells of Cajal / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D011706:Pyloric Antrum / Q000187:drug effects / Q000502:physiology; D012844:Sincalide / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: C090019:8-sulfocholecystokinin octapeptide; D054815:Cyclic Nucleotide-Gated Cation Channels; D005765:Gastrointestinal Agents; D012844:Sincalide; D002118:Calcium