Figure 6.

Effect of AR agonists on cAMP accumulation in isolated rat cardiomyocytes. In panels (a)–(c), cells were initially prestimulated for 5 min with the indicated concentrations of adenosine (a), CPA (b), and Cl-IB-MECA (c), prior to stimulation with 1.5 μM forskolin for 10 min in the absence (opened symbols) and presence (filled symbols) of PTX. Cells were pretreated with 100 ng ml⁻¹ PTX for 16 h to block G_i/G_o-protein-dependent pathways. Data are expressed as the percentage of the forskolin response (in the absence of agonist=100%). In panel (d), cells were stimulated with the indicated concentrations of CGS 21680 for 15 min in the absence of forskolin. Data are expressed as the percentage of the basal cAMP accumulation (100%). The results represent mean±s.e.m. of 4–6 independent experiments performed in duplicate. Standard error bars not shown are within the symbol.