Figure 2).

Scheme of the signal cascade with beta (β)₁-adrenergic receptor (AR) autoantibodies according to Freedman and Lefkowitz (adapted with permission from reference 17). The seven-membrane-spanning receptor is stimulated by the physiological agonist noradrena-line or by the immunoglobulin G (IgG) of β₁-AR autoantibodies from patients with dilated cardiomyopathy or chronic heart failure. This stimulation activates the G-protein-adenylyl cyclase (AC) system with known consequences for augmentation of Ca²⁺, activation of contractility and, finally, destruction of cardiomyocytes. CaMK II Calcium/calmodulin-dependent protein kinase II; cAMP Cyclic AMP; EC II Extracellular loop II; GRK2ct G-protein-coupled receptor kinase 2 C terminus; PKA Protein kinase A; PLB Phospholamban; RyR Ryanodine receptor