A) Isolated adult cardiomyocytes treated with M119 (10 μM) show enhanced cAMP generation at baseline and in response to Iso stimulation. B, C) M119 (10 μM) interferes with β-AR induced GRK2 membrane recruitment. Representative western blot analysis of GRK2 protein level in membrane fractions of cardiomyocytes treated with vehicle alone, Iso, M119, or M119 and Iso. Positive control lane of proteins from HEK293 cells transfected with GRK2 (B). Densitometric analysis of GRK2 membrane recruitment from four independent experiments demonstrates that M119 leads to ~50% decrease in Iso-induced GRK2 membrane recruitment (C). *P<.05, **P<.01, ***P<.001