The calcium-related basis of action of adenosine in rabbit aortic smooth muscle

1. In rabbit aortic smooth muscle, adenosine inhibited the increase induced by norepinephrine (NE) in 45Ca uptake in the presence of KCl (under low affinity Ca2+ uptake conditions) and the NE-induced decrease in 45Ca uptake (under high affinity Ca2+ uptake conditions). Basal 45Ca uptake and KCl-stimulated 45Ca uptake were not altered by adenosine. 2. Adenosine blocked the NE-induced contraction (in high K+) and inhibited both the tonic and phasic components of the NE-induced contraction. 3. Thus, adenosine selectively inhibits release of the intracellular Ca2+ store important for the phasic response to NE and that Ca2+ uptake component important for the NE-induced tonic response.