Role of nitric oxide, cyclic GMP and superoxide in inhibition by adenosine of calcium current in rabbit atrioventricular nodal cells.
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.
Martynyuk
A E
AE
Department of Medical Cardiology, Royal Infirmary, Glasgow, UK.
Kane
K A
KA
Cobbe
S M
SM
Rankin
A C
AC
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
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