Influence of receptor number on the stimulation by salmeterol of gene transcription in CHO-K1 cells transfected with the human beta2-adrenoceptor.
1. The beta2-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 beta2-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 beta2-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-beta2/6), 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-beta2/ 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-beta2/4 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.
McDonnell
J
J
Institute of Cell Signalling and School of Biomedical Sciences, Medical School, Queen's Medical Centre, Nottingham.
Latif
M L
ML
Rees
E S
ES
Bevan
N J
NJ
Hill
S J
SJ
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000420:Albuterol / Q000031:analogs & derivatives* / Q000494:pharmacology; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D020120:Iodocyanopindolol / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D018343:Receptors, Adrenergic, beta-2 / Q000235:genetics / Q000378:metabolism*; D000068299:Salmeterol Xinafoate; D014158:Transcription, Genetic / Q000187:drug effects*; D014162:Transfection
D000318:Adrenergic beta-Agonists; D018343:Receptors, Adrenergic, beta-2; D000068299:Salmeterol Xinafoate; D020120:Iodocyanopindolol; D000242:Cyclic AMP; D000469:Alkaline Phosphatase; D007545:Isoproterenol; D000420:Albuterol