Biochemical and autoradiographic analysis of β-adrenoceptors in rat nasal mucosa

The specific binding of 125I-(−)-cyanopindolol ( 125I-(−)-CYP) to homogenates and cryostat sections of rat nasal mucosa was saturable, stereoselective and of high affinity (K d = 5.0 ± 0.4 pM, B max = 204 ± 12 fmol/mg protein and K d = 7.2 ± 0.7 pM; B max = 15 ± 1 fmol/mg protein respectively). The subtype-selective antagonists, LK203-030 and ICI118,551, inhibited specific 125I-(−)-CYP binding according to a two-binding site model, indicating the presence of 57 and 45% β 1-adrenoceptors in homogenates and cryostat sections, respectively. Competition of isoprenaline for antagonist binding to homogenates demonstrated 30 ± 3% high-affinity agonist binding sites. A steepening of the curve was observed in presence of guanine nucleotides. In vitro labelling of cryostat sections of rat nasal mucosa was combined with autoradiography. The autoradiographs generated after incubation with 20 pM 125I-(−)-CYP showed specific labelling of the epithelium and glandular excretory ducts. It appeared from autoradiographs generated with subtype-selective antagonists in addition to the radioligand that β 1-and β 2-adrenoceptors were present in both structures.