Figure 5.

Activation of A₃ receptors by endogenous adenosine prevented the effect of inosine in 15 mM K⁺. (A) Inosine (100 μM) failed to reduce asynchronous ACh release induced by 15 mM K⁺ (n = 5). (B) The inhibition of the production of adenosine by 100 μM αβ-MeADP (inhibitor of ecto-5′-nucleotidase, n = 4) allowed the effect of 100 μM inosine on 15 mM K⁺-evocked ACh release. (C) Blockade of A₃ receptors with the selective antagonist MRS-1191 (5 μM) prevented the inhibitory action of endogenous nucleosides and further increased MEPP frequency in 15 mM K⁺ (n = 4). Data (mean ± SEM) are expressed as percentage of control values. **P < 0.01, *P < 0.05, anova followed by Tukey's test.