The effects of adenosine, ATP and ADP on ventricular automaticity induced by a local injury in the isolated right ventricle of the rat.

The effects of adenosine, adenosine triphosphate (ATP) and adenosine diphosphate (ADP) on ventricular automaticity induced by a local injury have been studied in the isolated right ventricle of the rat. Adenosine in low concentrations (10(-10)--10(-8) M) increased ventricular automaticity but in high concentrations (10(-5)--10(-4) M) decreased it. ATP and ADP decreased consistently ventricular automaticity, ATP being more effective than ADP. Theophylline in a concentration (5 X 10(-4) M) devoid of effect on ventricular automaticity antagonized both the excitatory and the inhibitory effects of adenosine. A high calcium solution (5.4 mM calcium) also prevented both the excitatory and the inhibitory effects of adenosine. The results suggest that adenosine in low concentrations might contribute to ventricular dysrhythmias, and that ATP and ADP as well as high concentrations of adenosine might have antidysrhythmic effects. The effects of adenosine appear to be mediated through calcium-dependent theophylline-sensitive receptors: the high affinity receptor operating the excitatory effect and the low affinity adenosine receptor operating the adenosine inhibitory effect on ventricular automaticity.