Dexamethasone potentiates high-affinity beta-agonist binding and g(s)alpha protein expression in airway smooth muscle.
Corticosteroids enhance beta-adrenergic responses by actions at both beta-adrenoceptor (beta-AR) and post-beta-AR sites. The present study investigated the effects of dexamethasone on beta-AR density, high-affinity beta-agonist binding, G(s)alpha and G(i)alpha protein expression, and cAMP responses in bovine tracheal smooth muscle (bTSM). Dexamethasone treatment of cultured bTSM cells increased total beta-AR density 1.6- to 1.9-fold as assessed by the saturation binding of [(3)H]CGP-12177 and by displacement of radioligand binding with isoproterenol. Isoproterenol bound to the beta-AR at two sites, a high-affinity site with a density of 5.9 +/- 1.2 fmol/mg protein and a low-affinity site with a density of 16.9 +/- 1. 0 fmol/mg protein. Dexamethasone increased both high- and low-affinity isoproterenol binding sites to 11.1 +/- 2.2 and 25.9 +/- 2.1 fmol/mg protein, respectively, without influencing agonist binding affinities. Dexamethasone also selectively increased G(s)alpha protein levels from 0.99 +/- 0.14 to 1.46 +/- 0.17 microg/mg protein without affecting G(i)alpha levels. The net effect of these changes was a 1.8-fold increase in maximal isoproterenol-induced cAMP generation in dexamethasone-treated bTSM cells. These findings provide new insights into the corticosteroid regulation of beta-adrenergic signaling pathways in airway smooth muscle.
Kalavantavanich
K
K
Pediatric Pulmonary Division, University of Connecticut School of Medicine, Farmington, Connecticut 06030, USA.
Schramm
C M
CM
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D003907:Dexamethasone / Q000494:pharmacology*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000032:analysis / Q000378:metabolism*; D005938:Glucocorticoids / Q000494:pharmacology*; D007545:Isoproterenol / Q000494:pharmacology; D008024:Ligands; D008565:Membrane Proteins / Q000032:analysis / Q000378:metabolism; D009130:Muscle, Smooth / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D011412:Propanolamines / Q000494:pharmacology*; D011869:Radioligand Assay; D014132:Trachea / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D014316:Tritium
D000318:Adrenergic beta-Agonists; D005938:Glucocorticoids; D008024:Ligands; D008565:Membrane Proteins; D011412:Propanolamines; D014316:Tritium; D003907:Dexamethasone; D019205:GTP-Binding Protein alpha Subunits, Gs; D007545:Isoproterenol; C033394:CGP 12177