Functional evidence for the presence of adenosine A2-receptors in cultured coronary endothelial cells.

Adenosine and the adenosine receptor agonists, R- and S-N6-phenylisopropyladenosine (R- and S-PIA) and 5'-N-ethylcarboxamidoadenosine (NECA), enhanced [3H]cAMP accumulation in [3H]adenine-labelled cultured endothelial cells isolated from the microvasculature of guinea pig hearts. As shown by their concentration-response curves, NECA was a more potent agonist than R-PIA or adenosine. Their respective concentrations at half-maximal stimulation of [3H]cAMP accumulation were 0.7 microM, 10.5 microM and 12.6 microM, indicating a 15- to 18-fold potency difference between NECA and the other agonists. The increased [3H]cAMP accumulation elicited by 10(-5) M NECA was inhibited by the xanthine derivative 8-phenyltheophylline, 3-isobutyl-1-methylxanthine, theophylline or caffeine. These findings provide functional evidence for the presence of adenosine receptors of the A2-type in microvascular coronary endothelial cells in culture. The functional significance of these receptors remains to be established, but they may be involved in the regulation of vascular permeability.