Adenosine antagonizes the positive inotropic action mediated via β-, but not α-adrenoceptors in the rabbit papillary muscle

Abstract

In the isolated rabbit papillary muscle, adenosine (1–300 μM) alone scarcely affected the basal tension developed. The positive inotropic action of isoprenaline, mediated via β-adrenoceptors, was inhibited by adenosine in a concentration-dependent manner. Atropine (0.3 μM) abolished the inhibitory action of carbachol on the isoprenaline-induced positive inotropic action but did not affect the inhibitory action of adenosine. Adenosine failed to inhibit the positive inotropic action exerted by phenylephrine via stimulation of α-adrenoceptors in the presence of pindolol (30 nM). The present results indicate that the positive inotropic action was mediated via α-adrenoceptors whose subcellular mechanism was not susceptible to the inhibitory action of adenosine as are β-adrenoceptors.