Unchanged G-protein-coupled receptor kinase activity in the aging human heart

Objectives We sought to find out whether G-protein-coupled receptor kinase (GRK) activity is also increased in the aging human heart. Background In the aging and failing human heart, cardiac beta-adrenoceptors (beta-AR) are desensitized. In heart failure (HF), an increase in cardiac GRK activity considerably contributes to this beta-AR desensitization. Methods We assessed GRK activity (by in vitro rhodopsin phosphorylation) in the right atria (RA) from 16 children (mean age 9 ± 2 years) and 17 elderly patients (mean age 67 ± 2 years) without apparent HF and in the RA from four patients with end-stage HF. Results Cytosolic and membranous GRK activities in the RA from children were not significantly different from those in elderly patients; in contrast, cytosolic and membranous GRK activities in the RA from patients with end-stage HF were significantly increased. Conclusions In contrast to the failing human heart, in the aging human heart, GRK activity is not increased. Thus, GRK activity appears to not play an important role in beta-AR desensitization in the aging human heart.