Table 2

Efficacies and potencies of β₂AR ligands at the GTPase of β₂ARG_sα and β₂AR_CAMG_sα

Parameter	β₂ARG_sα	β₂AR_CAMG_sα
Efficacy
(−)-ISO	1.00	1.00
(⁺)-ISO	0.91 ± 0.03	0.96 ± 0.04^n.s.
SAL	0.95 ± 0.02	0.99 ± 0.03^n.s.
DOB	0.76 ± 0.04	0.82 ± 0.04^2-150
EPH	0.66 ± 0.05	0.76 ± 0.06^2-150
DCI	0.49 ± 0.08	0.58 ± 0.02^2-150
EC₅₀ (nM)
(−)-ISO	13 ± 3	2.4 ± 1.1^2-150
(⁺)-ISO	150 ± 15	27 ± 12^2-150
SAL	93 ± 10	21 ± 10^2-150
DOB	90 ± 19	19 ± 9^2-150
EPH	560 ± 180	544 ± 150^2-150
DCI	29 ± 4	17 ± 4^2-150

GTPase activity was measured as described under Experimental Procedures in Sf9 membranes expressing various β₂ARG_sα and β₂AR_CAMG_sα. Reaction mixtures contained β₂AR ligands at 0.1 nM–1mM as appropriate to obtain saturated concentration-response curves. Ligand efficacies and potencies (EC₅₀ values) were obtained by nonlinear regression analysis of the concentration-response curves shown in Figs. 3 and 4. The efficacy of (−)-ISO was set 1.00, and the effects of other ligands are referred to this effect. Data shown are the means ± S.D. of three to seven independent experiments performed in duplicate. The data shown for β₂ARG_sαwere previously reported in Seifert et al. (1999a). Data for β₂ARG_sα were compared versus β₂AR_CAMG_sα using the t test.

↵2-150 p < 0.05;
^n.s. not significant.