Estimation of β adrenergic receptor (AR) subtypes by single-point saturation binding assay in tracheobronchial smooth muscle of (A) wild-type (WT) C57BL/6J, (B) β-arrestin-1 knockout (βarr1 KO), and (C) β-arrestin-2 knockout (βarr2 KO) mice.

The competitive displacement of the non-selective radiolabeled antagonist (¹²⁵I)-cyanopindalol (CYP) (500 pM) by 500 nM CGP-20712A and 100 nM ICI-118551 quantifies the proportions of β₁AR and β₂AR, respectively. Propranolol, a nonselective βAR blocker, gives a measure of total βAR present in each tissue. A. WT: β₁AR = 12 ± 5%; β₂AR = 64 ± 3%; 100% corresponds to 208.2 ± 28 fmol/mg. B. βarr1 KO: β₁AR = 13 ± 4%; β₂AR = 60 ± 4%; 100% corresponds to 213 ± 55 fmol/mg. C. βarr2 KO: β₁AR = 14 ± 4%; β₂AR = 65 ± 2%; 100% corresponds to 255.7 ± 82 fmol/mg. Data represent the mean ± SEM of 3 independent experiments performed in quadruplicate.