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

Abstract

Abstract 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 (> 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. Similarly, 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.