Adenosine and Coronary Vascular Pharmacology

It is generally accepted that adenosine plays an important role in the regulation of coronary blood flow by producing vasorelaxation. This effect has been proposed to be mediated predominantly by extracellular A2 adenosine receptors which are coupled to various effector systems via G-proteins (1). In the vascular smooth muscle, activation of the A2 adenosine receptors has been shown to induce augmentation of cAMP production, hyperpolarization of cell membrane, and inhibition of calcium fluxes and phosphoinositide metabolism. However, recent evidence indicate that the coronary adenosine receptors are more complex and may involve the participation of various other factors. There are reports indicating that A2 adenosine receptors may also be located on the coronary endothelium, mediating endothelium-dependent responses, and the smooth muscle may also contain other types of adenosine receptors, including A1 adenosine receptors which are coupled to adenylate cyclase and PKC-mediated responses (2,3). In this chapter, we review the status of the coronary smooth muscle and endothelial adenosine receptors mediating relaxation, and the regulation of PKC in coronary artery by adenosine agonists, based on our recent data.