Regulation of adrenoceptors and G protein-coupled receptor kinases (GRKs). 1: β-adrenoceptor location; 2: activation; 3: signaling through G proteins with adenylate cyclase (AC) activation; 4: phosphorylation by GRKs; 5: endocytosis; 6: location of endosomes; 7: recycling to the membrane; 8: degradation in lysosomes.