title: Role of nitric oxide, cyclic GMP and superoxide in inhibition by adenosine of calcium current in rabbit atrioventricular nodal cells.
abstract: OBJECTIVE
  To study the intracellular pathways which mediate the inhibitory actions of adenosine on isoprenaline-stimulated calcium current (ICa) in atrioventricular (AV) nodal myocytes.
  
  
  METHODS
  The whole-cell patch-clamp technique was used to record ICa from rabbit AV nodal cells, isolated by enzymatic and mechanical dispersion.
  
  
  RESULTS
  Isoprenaline, 0.1 microM, increased peak ICa from 0.58 +/- to 1.23 +/- 0.1 nA, and this increase was reversibly inhibited by adenosine, 10 microM (83 +/- 6%), which we have previously shown to be mediated by nitric oxide (NO) production. A membrane-permeable analogue of cyclic GMP, 8-Br-cGMP (300 microM), an inhibitor of cGMP-stimulated phosphodiesterase, prevented the effect of adenosine on ICa-Methylene blue (10 microM), an inhibitor of NO-sensitive guanylyl cyclase and a generator of superoxide (.02-), did not prevent, but increased, the inhibiting action of adenosine (49.5 +/- 6.6%, P < 0.01). Methylene blue (50 microM) caused a reduction of ICa, with further inhibition when combined with adenosine. A .O(2-)-generating system, xanthine oxidase (0.02 U/ml) and purine (2.3 mM), also increased the inhibitory action of adenosine on ICa. Inhibition of ICa by adenosine in the presence of xanthine oxidase was not prevented by 8-Br-cGMP (300 microM) and was not influenced by pre-incubation of cells with a NO synthase inhibitor, L-NAME (0.5 mM).
  
  
  CONCLUSIONS
  The inhibitory effect of adenosine on ICa in rabbit AV nodal myocytes can be mediated by two mechanisms--stimulation of cGMP-stimulated phosphodiesterase by NO-induced cGMP, and a mechanism which involves interaction with .O2- production.
authors.affiliation: Department of Medical Cardiology, Royal Infirmary, Glasgow, UK.
authors.forename: A E
authors.initials: AE
authors.lastname: Martynyuk
authors.forename: K A
authors.initials: KA
authors.lastname: Kane
authors.forename: S M
authors.initials: SM
authors.lastname: Cobbe
authors.forename: A C
authors.initials: AC
authors.lastname: Rankin
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000241:Adenosine / Q000494:pharmacology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D001283:Atrioventricular Node / Q000187:drug effects*; D000252:Calcium-Transporting ATPases / Q000187:drug effects*; D002469:Cell Separation; D004396:Coloring Agents / Q000494:pharmacology; D006152:Cyclic GMP / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology; D008751:Methylene Blue / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D013481:Superoxides; D014969:Xanthine Oxidase / Q000494:pharmacology
chemical_list: D000318:Adrenergic beta-Agonists; D000889:Anti-Arrhythmia Agents; D004396:Coloring Agents; D013481:Superoxides; D015124:8-Bromo Cyclic Adenosine Monophosphate; D009569:Nitric Oxide; D014969:Xanthine Oxidase; D000252:Calcium-Transporting ATPases; D006152:Cyclic GMP; D000241:Adenosine; D007545:Isoproterenol; D008751:Methylene Blue