Adenosine A2A and A2B receptors mediated nitric oxide production in coronary artery endothelial cells

The present study further examined the functional presence and the signal transduction mechanism(s) for adenosine A_2A and A_2B receptors through nitric oxide (NO) and the guanosine 3′, 5′-cyclic monophosphate (cGMP) pathway in cultured porcine coronary artery endothelial cells (PCAEC). The application of adenosine receptor agonists, NECA, CGS-21680 and CAD between 10⁻⁷ and 10⁻⁴ M, enhanced the production of NO (measured as nitrite) in a dose-dependent manner. On the basis of EC₅₀ values, these agonists showed the following order of potency: NECA>CGS-21680>CAD. This order appears to be of the A₂ adenosine receptor subtype. Similarly, the same concentrations of adenosine agonists evoked the production of cGMP in a dose-dependent manner, exhibiting a rank order that is similar to that of NO production. NO synthase inhibitor, N-nitro-l-arginine methylester (l-NAME, 10⁻⁵ M), inhibited the production of NO and cGMP, which was reversed by l-arginine (10⁻⁴ M). Selective A_2A adenosine receptor antagonists, ZM-241385 and SCH-58261, at 10⁻⁷ M, significantly inhibited the effects of CGS-21680, but only partly inhibited the effect of NECA on NO and cGMP production. Along with the earlier molecular evidence from this laboratory [Am. J. Physiol. 279 (2000) H650], the present data further support the presence of both A_2A and A_2B receptors in PCAEC. These results further support that coronary endothelial cells express functional A_2A and A_2B adenosine receptors, leading to GMP production through the NO-synthase-linked mechanism. This is the first direct evidence where an A_2B adenosine receptor has been linked to NO production in cultured endothelial cells and could play a role in coronary artery physiology and pathophysiology.