Influence of receptor density and G protein expression on relative efficacy of clonidine
| Cell Line | Receptor Density | G Protein Activation by Clonidine |
|---|---|---|
| pmol/mg | % of max | |
| α2-AR no. 1 | 5.3 ± 0.5 | 40 ± 0.7 |
| α2-AR no. 2 | 25 ± 1.0 | 63 ± 1.4 |
| α2-AR/Giα1 | 36 ± 0.2 | 57 ± 5.0 |
| α2-AR/Goα1 no. 2 | 8.7 ± 0.5 | 95 ± 1.41-150 |
| α2-AR/Goα1 no. 3 | 2.0 ± 0.2 | 91 ± 3.71-150 |
G protein activation was determined by measuring agonist-induced increases in the binding of GTPγ35S in membrane preparations. Data are presented as mean ± S.E. derived from three to six experiments with duplicate determinations. Refer to Figs. 1B and 2C for the full dose-response curve for α2 AR no. 1, α2-AR/Giα1, and α2-AR/Goα1 no. 2 transfectants. Level of Goα1 expression was similar in both α2-AR + Goα1 no. 2 and α2-AR + Goα1 no. 3 transfectants.
% of max, compares response of clonidine to that of the maximal response achieved with the full agonist epinephrine (clonidine = 100 μM; epinephrine = 100 μM).
↵1-150 p < .01 α2-AR + Goα1cotransfectants versus α2-AR transfectants and α2-AR + Giα1 cotransfectants (one-way ANOVA). “No.” refers to independently isolated transfectants.