Table 1 Various adenosine receptors, their transducer pathways, location and actions

A1

Linked to Gi (subtype of heterotrimeric GTP binding protein). Decreases cAMP, increases potassium ion efflux and decreased calcium ion influx

Depressing effect on myocardium (Negative Dromotropy and Negative Chronotropy). Inhibits atrioventricular conduction, prolongs refractory period

A2A and A2B

Linked to Gs (subtype of heterotrimeric GTP binding protein). Increases cAMP (Cyclic Adenosine Monophosphate)

Causes vasodilation of myocardial microvasculature. Causes constriction of hepatic vein, renal vein and afferent arterioles of spleen. Causes inhibition of platelet activity

A3

Linked to Gi

Involved in ischemic preconditioning of myocardium. Involved in promoting inflammation by attracting white blood cells; specifically neutrophils (chemo-kinesis)