© 2003 by European Society of Cardiology
Copyright © 2003, European Society of Cardiology
New insights into β2-adrenoceptor signaling in the adult rat heart
Max Delbrück Center for Molecular Medicine, Robert Rössle Strasse 10, D-13125 Berlin, Germany
s.bartel{at}mdc-berlin.de
* Corresponding author. Tel.: +49-30-9406-2519; fax: +49-30-9406-2110.
Objective: The role of cAMP in β2-adrenoceptor signaling and its functional relevance in adult rat heart has been the subject of considerable controversy. Therefore, we investigated the β2-adrenoceptor pathways in both adult cardiomyocytes and in the intact hearts of Wistar rats with respect to protein kinase A (at Ser16)-, the key event in shortening of relaxation time, and CaM kinase II (at Thr17)-dependent phospholamban phosphorylation. Methods: Contractile and cellular β1/β2-adrenergic responses were studied in parallel on the same perfused rat heart. (–)Isoproterenol and the β2-adrenergic agonists zinterol and procaterol were used to discriminate the β-adrenoceptor subtype-related actions. Results: β2-Adrenoceptor stimulation induces protein kinase A-dependent phospholamban phosphorylation in both adult cardiomyocytes and in adult hearts of rats. The β2-adrenoceptor-mediated shortening of relaxation time in the heart correlates with Ser16 phosphorylation. Adenosine elicited antiadrenergic action on both β1- and β2-adrenergic signaling cascades by reducing the phosphorylation status of phospholamban. Only β1-adrenoceptor stimulation produced significant CaM kinase II-related Thr17 phosphorylation, troponin I phosphorylation and activation of phosphorylase a. Conclusions: Our findings clearly show that β2-adrenoceptor signaling is coupled to phospholamban phosphorylation and shortening of relaxation time in the adult rat heart.
KEYWORDS Adrenergic (ant)agonists; Myocytes; Receptors; Signal transduction