Influence of receptor number on the stimulation by salmeterol of gene transcription in CHO-K1 cells transfected with the human β2-adrenoceptor

1 The beta(2)-agonist salmeterol is a potent relaxant of airway smooth muscle with a long duration of action. Previous studies of cyclic AMP accumulation, however, have indicated that salmeterol is a low efficacy beta(2)-agonist when compared to isoprenaline. Here we have compared the properties of salmeterol and isoprenaline as stimulants of gene transcription in CHO-K1 cells transfected with the human beta(2)-adrenoceptor to different levels (50 and 310 fmol mg protein(-1)). 2 Gene transcription was monitored using a secreted placental alkaline phosphate (SPAP) reporter gene under the transcriptional control of six cyclic AMP response element (CRE) sequences. 3 In the lower expressing cells (CHO-beta(2)/6), salmeterol produced a maximal cyclic AMP response that was only 22% that of that obtained with isoprenaline. In contrast in the higher expressing cells (CHO-beta(2)/4), the two maxima were of similar magnitude. 4 Salmeterol was a more potent stimulant of gene transcription, producing the same maximal response as isoprenaline in both cell lines. Furthermore, in the CHO-beta(2)/4 cells, Salmeterol was 50 fold more potent as a stimulant of SPAP secretion than of cyclic AMP accumulation. In contrast, isoprenaline was 24 fold less sensitive as a stimulant of SPAP secretion than of cyclic AMP accumulation. In the presence of serum (10%), the effects of both salmeterol and isoprenaline on gene transcription were augmented. 5 These data suggest that the low efficacy and/or long duration of action of salmeterol, favours a potent stimulation of gene transcription when compared to more efficacious but shorter-lived agonists such as isoprenaline.