Characterization of beta-adrenergic receptors in cultured bovine tracheal gland cells.

We characterized the beta-adrenergic receptors that mediate secretory responses to isoproterenol in cultured bovine tracheal submucosal gland cells. Previous studies have shown that these cells have morphological and biochemical features characteristic of serous cells. Isoproterenol, epinephrine, and norepinephrine each stimulated the secretion of 35SO4-labeled macromolecules from these cultured serous cells with a rank order of potency (isoproterenol greater than epinephrine greater than norepinephrine) consistent with the presence of beta 2-adrenergic receptors. These functional studies were supported by radioligand-binding studies using [I125]-iodocyanopindolol (125I-CYP) to identify beta-adrenergic receptors. 125I-CYP binding to membrane particulates prepared from cultured serous cells was saturable and of high affinity (equilibrium dissociation constant 20 +/- 3 pM; mean +/- SE, n = 6) and was antagonized stereoselectively by propranolol. Adrenergic agonists competed for 125I-CYP-binding sites with a rank order of potency characteristic of the beta 2-adrenergic receptor subtype. A specific beta 2-adrenergic receptor antagonist, ICI 118.551, competed for a single class of 125I-CYP-binding sites with high affinity (inhibition constant 1.8 +/- 0.3 nM, n = 3). We concluded that the secretory response of cultured tracheal gland cells to isoproterenol is a response mediated by beta-adrenergic receptors of the beta 2 subtype.