| Research Abstract |
Nitric oxide (NO), a possible cardioprotective substance, increase the production of interstitial adenosine in the rat ventricular myocardium.
With the use of microdialysis techniques, we assessed the activity of ecto-5'-nucleotidase in in vivo rat heart, and investigated the effects of nitric oxide (NO) on the production of interstitial adenosine in the ventricular myocardium. Dialysate adenosine obtained during perfusion with the AMP-containing solution through the probe originated from the hydrolysis of AMP by endogenous ecto-5'-nucleotidase, and the level of adenosine reflected the activity of ecto-5'-nucleotidase in the tissue. The present study demonstrated that tyramine released norepinephrine (NE) elevates adenosine via stimulation of αィイD21ィエD2-aderenoceptor and protein kinase C-mediated activation of ecto-5'-nucleotidase in rat heart. Therefore, reserpine-induced NE depletion suppressed tyramine-induced adenosine. On the other hand, singlet oxygin, (ィイD11ィエD1OィイD22ィエD2), cause
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s inactivation of ecto-5'-nucleotidase and decrease the concentration of adenosine. We confirmed that opening of cardiac an ATP sensitive KィイD1+ィエD1(KィイD2ATPィエD2) channels may causes ・OH generation. NOS, a NO synthase, inhibition is associated with cardioprotective effect due to the suppression of potassium ion concentration, [KィイD1+ィエD1]ィイD20ィエD2, depolarization-induced hydroxyl radical (・OH) generation. S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, increased the dialysate adenosine measured in the presence of AMP (100μM) in a concentration-dependent manner. In the presence of an NO oxidizing agent, 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (Carboxy-PTIO), the effect of SNAP was abolished. Another NO donor, FK409 also increased adenosine production. 8-Bromo-cGMP, a membrane permeable cGMP analogue and a potent activator of cGMP-dependent protein kinase increased the level of AMP-primed dialysate adenosine in a concentration-dependent manner. These results suggest that NO facilitates the production of interstitial adenosine in rat hearts in situ, via cGMP mediated stimulation of ecto-5'-nucleotidase, a de novo pathway of adenosine production. Less
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