title: Characterization of ouabain-induced noradrenaline and acetylcholine release from in situ cardiac autonomic nerve endings.
abstract: OBJECTIVE
  Although ouabain modulates autonomic nerve ending function, it is uncertain whether ouabain-induced releasing mechanism differs between in vivo sympathetic and parasympathetic nerve endings. Using cardiac dialysis, we examined how ouabain induces neurotransmitter release from autonomic nerve ending.
  
  
  METHODS
  Dialysis probe was implanted in left ventricle, and dialysate noradrenaline (NA) or acetylcholine (ACh) levels in the anaesthetized cats were measured as indices of neurotransmitter release from post-ganglionic autonomic nerve endings.
  
  
  RESULTS
  Locally applied ouabain (100 microm) increased in dialysate NA or ACh levels. The ouabain-induced increases in NA levels remained unaffected by cardiac sympathetic denervation and tetrodotoxin (Na+ channel blocker, TTX), but the ouabain-induced increases in ACh levels were attenuated by TTX. The ouabain-induced increases in NA levels were suppressed by pretreatment with desipramine (NA transport blocker) and augmented by reserpine (vesicle NA transport blocker). In contrast, the ouabain-induced increases in ACh levels remained unaffected by pretreatment with hemicholinium-3 (choline transport blocker) but suppressed by vesamicol (vesicle ACh transport blocker). The ouabain-induced increases in NA levels were suppressed by pretreatment with omega-conotoxin GVIA (N-type Ca2+ channel blocker), verapamil (L-type Ca2+ channel blocker) and TMB-8 (intracellular Ca2+ antagonist). The ouabain-induced increases in ACh levels were suppressed by pretreatment with omega-conotoxin MVIIC (P/Q-type Ca2+ channel blocker), and TMB-8.
  
  
  CONCLUSIONS
  Ouabain-induced NA release is attributable to the mechanisms of regional exocytosis and/or carrier-mediated outward transport of NA, from stored NA vesicle and/or axoplasma, respectively, while the ouabain-induced ACh release is attributable to the mechanism of exocytosis, which is triggered by regional depolarization. At both sympathetic and parasympathetic nerve endings, the regional exocytosis is because of opening of calcium channels and intracellular calcium mobilization.
authors.affiliation: Department of Cardiac Physiology, National Cardiovascular Center Research Institute, Suita, Osaka, Japan. yamazaki@ri.ncvc.go.jp
authors.forename: T
authors.initials: T
authors.lastname: Yamazaki
authors.forename: T
authors.initials: T
authors.lastname: Akiyama
authors.forename: H
authors.initials: H
authors.lastname: Kitagawa
authors.forename: F
authors.initials: F
authors.lastname: Komaki
authors.forename: H
authors.initials: H
authors.lastname: Mori
authors.forename: T
authors.initials: T
authors.lastname: Kawada
authors.forename: K
authors.initials: K
authors.lastname: Sunagawa
authors.forename: M
authors.initials: M
authors.lastname: Sugimachi
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D001341:Autonomic Nervous System / Q000187:drug effects / Q000378:metabolism*; D002316:Cardiotonic Agents / Q000008:administration & dosage; D002415:Cats; D004305:Dose-Response Relationship, Drug; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D006321:Heart / Q000187:drug effects / Q000294:innervation*; D009206:Myocardium / Q000378:metabolism*; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D010042:Ouabain / Q000008:administration & dosage*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
chemical_list: D002316:Cardiotonic Agents; D018377:Neurotransmitter Agents; D010042:Ouabain; D000109:Acetylcholine; D009638:Norepinephrine