PT - JOURNAL ARTICLE AU - Leif Erik Vinge AU - Kjetil W. Andressen AU - Toril Attramadal AU - Geir Øystein Andersen AU - Mohammed Shakil Ahmed AU - Karsten Peppel AU - Walter J. Koch AU - Neil J. Freedman AU - Finn Olav Levy AU - Tor Skomedal AU - Jan-Bjørn Osnes AU - Håvard Attramadal TI - Substrate Specificities of G Protein-Coupled Receptor Kinase-2 and -3 at Cardiac Myocyte Receptors Provide Basis for Distinct Roles in Regulation of Myocardial Function AID - 10.1124/mol.107.035766 DP - 2007 Sep 01 TA - Molecular Pharmacology PG - 582--591 VI - 72 IP - 3 4099 - http://molpharm.aspetjournals.org/content/72/3/582.short 4100 - http://molpharm.aspetjournals.org/content/72/3/582.full SO - Mol Pharmacol2007 Sep 01; 72 AB - The closely related G protein-coupled receptor kinases GRK2 and GRK3 are both expressed in cardiac myocytes. Although GRK2 has been extensively investigated in terms of regulation of cardiac β-adrenergic receptors, the substrate specificities of the two GRK isoforms at G protein-coupled receptors (GPCR) are poorly understood. In this study, the substrate specificities of GRK2 and GRK3 at GPCRs that control cardiac myocyte function were determined in fully differentiated adult cardiac myocytes. Concentration-effect relationships of GRK2, GRK3, and their respective competitive inhibitors, GRK2ct and GRK3ct, at endogenous endothelin, α1-adrenergic, and β1-adrenergic receptor-generated responses in cardiac myocytes were achieved by adenovirus gene transduction. GRK3 and GRK3ct were highly potent and efficient at the endothelin receptors (IC50 for GRK3, 5 ± 0.7 pmol/mg of protein; EC50 for GRK3ct, 2 ± 0.2 pmol/mg of protein). The α1-adrenergic receptor was also a preferred substrate of GRK3 (IC50,7 ± 0.4 pmol/mg of protein). GRK2 lacked efficacy at both endothelin and α1-adrenergic receptors despite massive overexpression. On the contrary, both GRK2ct and GRK3ct enhanced β1-adrenergic receptor-induced cAMP production with comparable potencies. However, the potency of GRK3ct at β1-adrenergic receptors was at least 20-fold lower than that at endothelin receptors. In conclusion, this study demonstrates distinct substrate specificities of GRK2 and GRK3 at different GPCRs in fully differentiated adult cardiac myocytes. As inferred from the above findings, GRK2 may play its primary role in regulation of cardiac contractility and chronotropy by controlling β1-adrenergic receptors, whereas GRK3 may play important roles in regulation of cardiac growth and hypertrophy by selectively controlling endothelin and α1-adrenergic receptors. The American Society for Pharmacology and Experimental Therapeutics