FIGURE 7.

Wild type and mutant β₂ARs differentially couple to G_i proteins to regulate agonist-induced contraction rate increases. A–C, the β₁β₂AR-KO cardiac myocytes expressing the β₂AR, PKAmut β₂AR, or GRKmut β₂AR were stimulated with 10 μm Iso in the presence or absence of PTX. The response in myocyte contraction rate was measured. D and E, the base-line levels of contraction rates and the maximal increases in contraction rates after stimulation in the presence or absence of PTX were plotted. ***, p < 0.001 when compared with the group without PTX treatment by two-way ANOVA. *, p < 0.05 when compared with the group without PTX treatment in Student's t test.