Interaction of Adenosine and Acetylcholine on the Bullfrog Atrium

抄録

As adenosine has a potent stabilizing action on catechol-amine stimulation in the myocardium, the mode of interaction of adeno-sine and acetylcholine (ACh) was studied with regard to the membrane potential, current and tension components of the bullfrog atrium, using the single or double-sucrose gap method. Adenosine (10-⁴-3×10-³ M) augmented the twitch contraction in the presence of ACh (10-⁹-5×10-⁷m) by lengthening the duration of the action potential. The dose-tension response curve for ACh was modified by adenosine, producing a rise of the inhibitory threshold of ACh, and the modification showed a non competitive interaction of these compounds. Under the voltage clamp, ACh-induced steady current (I_ACh) was inhibited by adenosine non-competitively. The known inhibition of slow inward current (I_s) by ACh was enhanced by adenosine, while the delayed outward current (I_x) was markedly suppressed. I_s-dependent and -independent tension com-ponents were both inhibited by adenosine, thereby suggesting a decrease in intracellular concentrations of calcium. The potent suppression of I_ACh and I_x induced by adenosine, however, appeared to mitigate the inhibitory action of ACh on the action potential and twitch contraction.