Fig 1. Cardiomyocyte contraction response to epinephrine or norepinephrine under different stimulation conditions.

Cardiac myocytes isolated from β1AR knockout mice that express endogenous β₂AR were stimulated with 10 μM epinephrine (Epi) or norepinephrine (NE) for 10 min and then re-challenged with (B, D) or without (A, C) Epi or NE for 60 min. The Epi- (A, B) or NE- (F, H) induced contraction rates were recorded. Data are shown as means ± SDs from three independent experiments.