Effects of a range of β2 adrenoceptor agonists on changes in intracellular cyclic AMP and on cyclic AMP driven gene expression in cultured human airway smooth muscle cells

1 The effects of the selective beta(2) adrenoceptor agonists salbutamol, terbutaline and salmeterol and the non-selective beta adrenoceptor agonist isoprenaline on [H-3]-cyclic AMP formation and cyclic AMP response element (CRE) driven luciferase expression, assessed using the construct p6CRE/luc, were studied in primary cultures of human airway smooth muscle (HASM) cells. 2 Optimal transfection conditions for transient expression of pGL3 Control were 4 mu g DNA/well(-1) in a 6 well plate and 1.8 mu l Transfectam/mu g DNA. Expression was maximal at 48-72 h. 3 Salbutamol (maximum response 19%, EC50 0.6 mu M), terbutaline (maximum response 38%, EC50 2.3 mu M) and salmeterol (maximum response 18%, EC50 0.0012 mu M) were all partial agonists for cyclic AMP formation compared with isoprenaline (EC50 0.08 mu M). However, all of the beta(2) adrenoceptor agonists produced increases in CRE-driven luciferase activity, in cultured HASM transfected with the vector p6CRE/luc, which were equivalent or greater (salmeterol) than those seen with isoprenaline. 4 Both salbutamol and salmeterol were more potent at increasing luciferase expression than in elevating cyclic AMP levels in these cells. The potency ratios (EC50 ((cyclic AMP))/EC50 ((LUC))) for the agents studied were isoprenaline: 0.2 fold, terbutaline: 3 fold, salbutamol: 24 fold, salmeterol: 38 fold. 5 These data suggest that important quantitative differences exist in the ability of beta(2) adrenoceptor agonists to increase whole cell cyclic AMP levels in airway smooth muscle and to drive gene expression via a CRE-driven mechanism.