Figure 1.

Cardiac adrenergic receptors and polymorphisms relevant to β-blocker responsiveness. Shown are the presynaptic α_2A- and α_2CARs that when activated by epinephrine or norepinephrine decrease norepinephrine release from the presynaptic nerve terminal. Presynaptic β₂AR activation increases norepinephrine release: on the cardiomyocyte, catecholamine activated β₁AR and β₂AR increase inotropy and chronotropy, and can under signal dampening due to receptor phosphorylation by GRKs (G-protein coupled receptor kinase).