title: Role of calcium-activated potassium currents in CNP-induced relaxation of gastric antral circular smooth muscle in guinea pigs.
abstract: OBJECTIVE
  To investigate ion channel mechanism in CNP-induced relaxation of gastric circular smooth muscle in guinea pigs.
  
  
  METHODS
  Spontaneous contraction of gastric smooth muscle was recorded by a four -channel physiograph. The whole cell patch-clamp technique was used to record calcium-activated potassium currents and membrane potential in the gastric myocytes isolated by collagenase.
  
  
  RESULTS
  C-type natriuretic peptide (CNP) markedly inhibited the spontaneous contraction in a dose-dependent manner in gastric circular smooth muscle in guinea pigs. Ly83583, an inhibitor of guanylate cyclase, weakened CNP-induced inhibition on spontaneous contraction but Zaparinast, an inhibitor of cGMP sensitive phosphoesterase, potentiated CNP-induced inhibition in gastric circular smooth muscles. The inhibitory effects of CNP on spontaneous contraction were blocked by tetrathylammonium (TEA), a nonselective potassium channel blocker. CNP hyperpolarized membrane potential from -60.0 mV+/-2.0 mV to -68.3 mV+/-3.0 mV in a single gastric myocyte. CNP increased calcium-activated potassium currents (I(K(ca))) in a dose-dependent manner in gastric circular myocytes. CNP also increased the spontaneously transient outward currents (STOCs). Ly83583 partly blocked CNP-induced increase of calcium-activated potassium currents, but Zaparinast potented the effect.
  
  
  CONCLUSIONS
  CNP inhibits spontaneous contraction, and potassium channel may be involved in the process in gastric circular smooth muscle of guinea pigs. CNP-induced increase of I(K(ca)) is mediated by a cGMP dependent pathway.
authors.affiliation: Department of Physiology, College of Medicine, Yanbian University, Yanji 133000, Jilin Province, China.
authors.forename: Hui-Shu
authors.initials: HS
authors.lastname: Guo
authors.forename: Zheng-Xu
authors.initials: ZX
authors.lastname: Cai
authors.forename: Hai-Feng
authors.initials: HF
authors.lastname: Zheng
authors.forename: Xiang-Lan
authors.initials: XL
authors.lastname: Li
authors.forename: Yi-Feng
authors.initials: YF
authors.lastname: Cui
authors.forename: Zuo-Yu
authors.initials: ZY
authors.lastname: Wang
authors.forename: Wen-Xie
authors.initials: WX
authors.lastname: Xu
authors.forename: Sang-Jin
authors.initials: SJ
authors.lastname: Lee
authors.forename: Young-Chul
authors.initials: YC
authors.lastname: Kim
mesh_terms: D000818:Animals; D004553:Electric Conductivity; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology*; D020098:Natriuretic Peptide, C-Type / Q000494:pharmacology*; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D011706:Pyloric Antrum / Q000187:drug effects* / Q000502:physiology*
chemical_list: D024681:Potassium Channels, Calcium-Activated; D020098:Natriuretic Peptide, C-Type