receptor agonist-induced cAMP activity in human airway smooth muscle cells. (A) The effects of dopamine (DA; 1 μM) or the dopamine D1-like receptor agonists (A68930 or SKF38393; 1 μM respectively) on cAMP production in cultured HASM cells. Number of experiments was shown in parentheses. (B) The effects of dopamine (1 μM) on cAMP production in the presence or absence of the dopamine D2 receptor antagonist (L-741626; 1 μM for 30 min pretreatment before dopamine treatment). N = 4. (C) Concentration-dependent effect of dopamine D1-like receptor agonist A68930 (1 nM - 100 μM) on cAMP production in cultured HASM cells. The cells were incubated with A68930 for 20 min before cAMP assay. N = 4 - 13. (D) Time-course effect of A68930 (1 μM) on cAMP production in cultured human airway smooth muscle cells. N = 6. (E) The effect of dopamine D1-like receptor selective antagonists SCH23390 or SCH39166 on A68930-stimulated cAMP production in HASM cells. Cells were pretreated with SCH23390 (1 μM) or SCH39166 (1 μM) for 30 min pretreatment prior to A68930 (1 μM) treatment for 20 min. Data represent means ± SEM. N = 7 - 9. *P < 0.05, **P < 0.01 and ***P < 0.001 compared with basal. ##P < 0.01 compared with A68930 alone. In each experiment, values were determined in triplicate.