The Inotropic Peptide βARKct Improves βAR Responsiveness in Normal and Failing Cardiomyocytes Through Gβγ-Mediated L-Type Calcium Current Disinhibition

• Published in: Circulation research 2011-01, Vol.108 (1), p.27-39
• Main Authors: Völkers, Mirko, Weidenhammer, Christian, Herzog, Nicole, Qiu, Gang, Spaich, Kristin, von Wegner, Frederic, Peppel, Karsten, Müller, Oliver J, Schinkel, Stefanie, Rabinowitz, Joseph E, Hippe, Hans-Jörg, Brinks, Henriette, Katus, Hugo A, Koch, Walter J, Eckhart, Andrea D, Friedrich, Oliver, Most, Patrick
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Vertebrates: cardiovascular system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/CIRCRESAHA.110.225201

RATIONALE:The Gβγ-sequestering peptide β-adrenergic receptor kinase (βARK)ct derived from the G-protein–coupled receptor kinase (GRK)2 carboxyl terminus has emerged as a promising target for gene-based heart failure therapy. Enhanced downstream cAMP signaling has been proposed as the underlying mechanism for increased β-adrenergic receptor (βAR) responsiveness. However, molecular targets mediating improved cardiac contractile performance by βARKct and its impact on Gβγ-mediated signaling have yet to be fully elucidated. OBJECTIVE:We sought to identify Gβγ-regulated targets and signaling mechanisms conveying βARKct-mediated enhanced βAR responsiveness in normal (NC) and failing (FC) adult rat ventricular cardiomyocytes. METHODS AND RESULTS:Assessing viral-based βARKct gene delivery with electrophysiological techniques, analysis of contractile performance, subcellular Ca handling, and site-specific protein phosphorylation, we demonstrate that βARKct enhances the cardiac L-type Ca channel (LCC) current (ICa) both in NCs and FCs on βAR stimulation. Mechanistically, βARKct augments ICa by preventing enhanced inhibitory interaction between the α1-LCC subunit (Cav1.2α) and liberated Gβγ subunits downstream of activated βARs. Despite improved βAR contractile responsiveness, βARKct neither increased nor restored cAMP-dependent protein kinase (PKA) and calmodulin-dependent kinase II signaling including unchanged protein kinase (PK)Cε, extracellular signal-regulated kinase (ERK)1/2, Akt, ERK5, and p38 activation both in NCs and FCs. Accordingly, although βARKct significantly increases ICa and Ca transients, being susceptible to suppression by recombinant Gβγ protein and use-dependent LCC blocker, βARKct-expressing cardiomyocytes exhibit equal basal and βAR-stimulated sarcoplasmic reticulum Ca load, spontaneous diastolic Ca leakage, and survival rates and were less susceptible to field-stimulated Ca waves compared with controls. CONCLUSION:Our study identifies a Gβγ-dependent signaling pathway attenuating cardiomyocyte ICa on βAR as molecular target for the Gβγ-sequestering peptide βARKct. Targeted interruption of this inhibitory signaling pathway by βARKct confers improved βAR contractile responsiveness through increased ICa without enhancing regular or restoring abnormal cAMP-signaling. βARKct-mediated improvement of ICa rendered cardiomyocytes neither susceptible to βAR-induced damage nor arrhythmogenic sarcoplasmic reticulum Ca leakage.