Inhibition of contractions and 45Ca influx by adenosine in rabbit aorta

The effects of adenosine on contractility and 45Ca-uptake in rabbit aorta have been examined and compared with those of nifedipine. Both adenosine (10(-5) M) and nifedipine (10(-8) M) inhibited contractions caused by CaCl2 (0.1-10 mM) in K(+)-depolarized preparations. Nifedipine (10(-7) M) significantly inhibited the contractions of noradrenaline (NA) at all doses (10(-8)-10(-4) M), while adenosine inhibited the contractions induced only by lower doses of NA (10(-8) and 10(-7) M) without affecting those at higher doses (greater than 10(-7) M). Adenosine (10(-8) M) and nifedipine (10(-7) M) inhibited K(+)-stimulated 45Ca-uptake by aortic strips by 75 and 100%, respectively. Similarity, NA (10(-4) M)-stimulated 45Ca influx was inhibited by about 70% by both these agents. The results suggest that adenosine inhibits inward Ca2+ movement involving both voltage-operated and receptor-operated calcium channels in rabbit aortic smooth muscle.