Antagonism of the positive dromotropic effect of isoproterenol by adenosine: role of nitric oxide, cGMP-dependent cAMP-phosphodiesterase and protein kinase G.
We hypothesized that nitric oxide (NO) plays an important role in mediating the anti-adrenergic effect of adenosine on atrioventricular (AV) nodal conduction. In guinea-pig hearts instrumented for measurement of AV nodal conduction time (atrium-to-His bundle, A-H, interval), the NO synthase (NOS) inhibitor, l-NMMA (100 microm), reversibly inhibited 80% (P=0.009, n=6) of adenosine's anti-adrenergic action on the positive dromotropic effect of isoproterenol (0.01 microm). In parallel studies carried out in rabbit AV nodal myocytes, intracellular mechanisms whereby NO mediates the inhibitory effect of adenosine on isoproterenol-induced A-H interval shortening were studied. Adenosine (3 microm) inhibited isoproterenol-stimulated (0.1 microm) I(Ca,L)(beta -I(Ca,L)) by 46+/-6% (P<0.001, n=17). Consistent with isolated heart data, the NOS inhibitors, l -NMMA (100 microm) and L-NNA (500 microm) attenuated the effect of adenosine on beta -I(Ca,L)by 69+/-8% (P<0.001, n=16) and 69+/-7% (P<0.001, n=10), respectively. An inhibitor of NO-stimulated guanylyl cyclase LY83538 (40 microm) reduced the inhibitory effect of adenosine on beta -I(Ca,L)by 97+/-6% (P=0.004, n=15). Similarly, the non-specific inhibitor of cAMP-phosphodiesterases IBMX (50 microm) decreased the anti-adrenergic effect of adenosine by 60% (P=0.02, n=6), whereas the extracellular application of the non-hydrolyzeable cAMP analog 8-Br-cAMP (500 microm) prevented this action of adenosine. Activation of cGMP-dependent protein kinase (PKG) by CPT-cGMP (300 microm) diminished beta -I(Ca,L), but to a significantly smaller degree (16+/-4%, P=0.025, n=12) than that caused by adenosine. NO mediates the anti-adrenergic effect of adenosine on AV nodal conduction by a mechanism predominately involving activation of cGMP-dependent cAMP-phosphodiesterase and to a lesser extent activation of PKG.
Zima
A
A
Department of Anesthesiology, University of Florida, Gainesville, FL, 32610, USA.
Martynyuk
A E
AE
Seubert
C N
CN
Morey
T E
TE
Sumners
C
C
Cucchiara
R F
RF
Dennis
D M
DM
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000502:physiology; D000241:Adenosine / Q000494:pharmacology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002463:Cell Membrane Permeability / Q000502:physiology; D002478:Cells, Cultured; D017869:Cyclic GMP-Dependent Protein Kinases / Q000502:physiology; D004336:Drug Antagonism; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology; D009569:Nitric Oxide / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D015398:Signal Transduction / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology*
D000318:Adrenergic beta-Agonists; D014665:Vasodilator Agents; D009569:Nitric Oxide; D017869:Cyclic GMP-Dependent Protein Kinases; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D000241:Adenosine; D007545:Isoproterenol