Effects of a range of β 2 adrenoceptor agonists on changes in intracellular cyclic AMP and on cyclic AMP driven gene expression in cultured human airway smooth muscle cells

The effects of the selective β 2 adrenoceptor agonists salbutamol, terbutaline and salmeterol and the non‐selective β adrenoceptor agonist isoprenaline on [ 3 H]‐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. Optimal transfection conditions for transient expression of pGL3 Control were 4 μg DNA/well 71 in a 6 well plate and 1.8 μl Transfectam/μg DNA. Expression was maximal at 48–72 h. Salbutamol (maximum response 19%, EC 50 0.6 μ M ), terbutaline (maximum response 38%, EC 50 2.3 μ M ) and salmeterol (maximum response 18%, EC 50 0.0012 μ M ) were all partial agonists for cyclic AMP formation compared with isoprenaline (EC 50 0.08 μ M ). However, all of the β 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. Both salbutamol and salmeterol were more potent at increasing luciferase expression than in elevating cyclic AMP levels in these cells. The potency ratios (EC 50 (cyclic AMP) /EC 50 (LUC) ) for the agents studied were isoprenaline: 0.2 fold, terbutaline: 3 fold, salbutamol: 24 fold, salmeterol: 38 fold. These data suggest that important quantitative differences exist in the ability of β 2 adrenoceptor agonists to increase whole cell cyclic AMP levels in airway smooth muscle and to drive gene expression via a CRE‐driven mechanism. British Journal of Pharmacology (1999) 128 , 721–729; doi: 10.1038/sj.bjp.0702829