Fig. 11.

ISO produces only potentiation after the inhibitory effects induced by purinergic, opioidergic, and β₂-adrenergic receptors. A, The cell was initially superfused with control external solution and then exposed to ATP (100 μm), DPDPE (1 μm), and DAMGO (10 μm), which caused inhibition. Addition of ISO (1 μm) caused no further depression but only a slow current potentiation. B, Sequential application of zinterol (1 μm) and ISO (1 μm) mimics the dual action of ISO shown in Figures 2C and 4B, proving that inhibition is mediated by β₂-ARs, whereas potentiation by ISO proceeds through β₁-ARs.Symbols, lettering, andtraces have the same meaning as in previous figures.