Fig. 4. Pharmacological and functional properties of wild-type ß₁AR and ß₁AR-GFP. BHK cells stably expressing ß₁AR () and ß₁ARGFP () at 0.7-1 pmol/mg protein were assayed for binding or cAMP accumulation as described in Materials and Methods. (A) Saturation binding of radioligand. Cell lysates were incubated for 3 hours at 30°C with increasing concentrations of ¹²⁵ICYP with or without 10 µM propranolol. K_d values for ICYP were 18.2±3.0 and 20.4±1.9 pM (P>0.05). (B) Antagonist competition binding. Same as A except 30 pM ¹²⁵ICYP and increasing concentrations of CGP-20712A were used. K_i values for CGP-2012A were 9.7±3.9 and 14.1±3.0 nM (P>0.05). (C) Agonist competition binding. Same as B except ISO plus 100 µM GTP were used. K_d values for ISO were 57.0±1.4 and 87.6±3.4 nM (P<0.002). (D) Cells were incubated with increasing concentrations of ISO or 100 µM forskolin for 10 minutes and assayed for cAMP. EC₅₀ values for ISO were 0.80±0.1 and 1.26±0.3 nM (P>0.05). V_max values for ISO as a percentage of forskolin stimulation were 74.7±1.3 and 50.0±3.6% (P<0.002). A representative experiment is shown in each panel. Values are the means±s.e.m. of 3 or 4 experiments.