Coronary and myocardial adenosine receptors

In the isolated guinea pig heart the rank oder of potency for coronary vasodilation is NECA greater than R-PIA greater than adenosine greater than S-PIA and this is characteristic for A2-adenosine receptors. Release of 3H-cyclic AMP from coronary endothelium in 3H-adenosine prelabeled hearts was augmented by these adenosine derivatives and followed the same rank order of potency. This identifies the coronary endothelial adenosine receptor to be of the A2-subtype. Similar results were obtained in bovine aortic endothelium in culture grown on microcarrier beads. Studies on isolated cardiac myocytes revealed, that adenosine derivatives did not alter basal cyclic AMP levels but attenuated the isoproterenol elicited increase, R-PIA being more potent than NECA. Thus, on cardiomyocytes the A1-adenosine receptor predominates and may be responsible for the antiadrenergic action of adenosine. Since vascular and cardiomyocyte adenosine receptors are of different subtypes this may be used as a specific marker to identify the origin of surface membranes prepared from cardiac tissue.