Am. J. Respir. Cell Mol. Biol., Vol 11, No. 3, 09 1994, 287-295.
Functional behavior of the beta-adrenergic receptor-adenylyl cyclase system in rabbit airway epithelium
IA Mardini, NC Higgins, S Zhou, JL Benovic and SG Kelsen
Department of Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania.
Stimulation of adenylyl cyclase mediates the effects of beta-adrenergic
agonists and prostaglandin E2 (PGE2) on tracheobronchial epithelial cell
function by increasing intracellular cyclic adenosine monophosphate (cAMP).
In turn, increases in cAMP affect airway function by modulating ciliary
beating, chloride and water transport, mucus secretion, and release of
bronchoactive substances. This study examined the function and regulation
of the beta-adrenergic receptor-adenylyl cyclase system (beta AR-AC) in
tracheal epithelial cells isolated from the rabbit, a frequently used
animal model of airway reactivity, inflammation, and electrolyte transport.
beta AR number, assessed by ligand binding using the non-subtype-specific
beta-antagonist [125I]iodopindolol, averaged approximately 10,700 beta
AR/cell (400 fmol/mg membrane protein). Greater than 85% of the receptors
were of the beta 2 subtype as determined by competitive antagonist
displacement of iodopindolol by selective beta 1- (betaxolol) and beta 2-
(ICI 118,551) antagonists. cAMP synthesis was stimulated with
isoproterenol, PGE2, and forskolin in a time- and concentration-dependent
fashion. Preincubation of epithelial cells for 30 min with either
isoproterenol (10 microM) or the peptide inflammatory mediator, bradykinin
(100 microM), markedly depressed subsequent isoproterenol-stimulated cAMP
synthesis. Isoproterenol-induced beta AR-AC desensitization appeared to be
homologous since cAMP responses to PGE2 and forskolin, a direct activator
of adenylyl cyclase, were not reduced. The effect of bradykinin on
isoproterenol-stimulated cAMP response was mimicked by preincubation with
either dioctanoyl glyceride or phorbol myristate acetate, activators of
protein kinase C.(ABSTRACT TRUNCATED AT 250 WORDS)
