β-adrenoceptors in human tracheal smooth muscle: characteristics of binding and relaxation |
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Authors: | Chris J van Koppen Marcel W Hermanussen Kiek N Verrijp Jaap F Rodrigues de Miranda Arie J Beld Jan-Willem J Lammers and Cees A M van Ginneken |
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Institution: | 1 Departments of Pharmacology and Pulmonary Diseases, University of Nijmegen P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands |
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Abstract: | Specific binding of 125I]-(?)-cyanopindolol to human tracheal smooth muscle membranes was saturable, stereo-selective and of high affinity (Kd=5.3±0.9 pmol/l and RT=78±7fmol/g tissue). The β1-selective antagonists atenolol and LK 203-030 inhibited specific 125I]-(?)-cyanopindolol binding according to a one binding site model with low affinity in nearly all subjects, pointing to a homogeneous β2-adrenoceptor population. In one subject using LK 203-030 a small β-adrenoceptor subpopulation could be demonstrated. The beta-mimetics isoprenaline, fenoterol, salbutamol and terbutaline recognized high and low affinity agonist binding sites. Isoprenaline's pKH- and pKL- values for the high and low affinity sites were 8.0±0.2 and 5.9±0.3 respectively. In functional experiments isoprenaline relaxed tracheal smooth muscle strips having intrinsic tone with a pD2-value of 6.63±0.19. |
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