title: Ser16-, but not Thr17-phosphorylation of phospholamban influences frequency-dependent force generation in human myocardium.
abstract: Beta-adrenoceptor/cAMP-dependent Ser16-phosphorylation as well as Ca(2+)-dependent Thr17-phosphorylation of phospholamban (PLB) influences SERCA 2a activity and thus myocardial contractility. To determine the cross-signaling between Ca2+ and cAMP pathways, the phosphorylation of Ser16-PLB and Thr17-PLB was studied at increasing stimulation frequencies as well as in the presence of beta-adrenergic stimulation in isolated ventricular trabeculae from failing (dilative cardiomyopathy, DCM, heart transplants, n=9) and non-failing human myocardium (donor hearts, NF, n=9). In addition, we measured the intracellular Ca(2+)-transient (fura-2) at increasing stimulation frequencies (0.5-3.0 Hz). Protein expression of SERCA 2a and phospholamban was similar in DCM and NF. In DCM, diastolic [Ca2+]i was increased and systolic [Ca2+]i as well as Ser16 PLB-phosphorylation were decreased as compared to NF at 0.5 Hz. The positive force-frequency relationship in human non-failing myocardium was accompanied by a frequency-dependent increase in Ser16-PLB, but not Thr17-PLB phosphorylation. In DCM, Ser16-PLB as well as Thr17-PLB phosphorylation were not altered at higher stimulation frequencies. After application of isoprenaline (1 microM), a profound increase in Ser16-PLB phosphorylation was accompanied by a small increase in Thr17-PLB phosphorylation, only in NF. The frequency-dependent phosphorylation of Ser16-PLB may favor an increase in Ca2+ transient and force generation in humans. Cross talk signaling of Ser16/Thr17-PLB phosphorylation after beta-adrenergic stimulation exists in non-failing, but not in failing human myocardium. The Ca(2+)-dependent CaM-kinase activity may be altered in human heart failure.
authors.affiliation: Laboratory of Muscle Research and Molecular Cardiology, Department of Internal Medicine III, University of Cologne, Joseph-Stelzmann-Str. 9, 50924 Cologne, Germany.
authors.forename: Klara
authors.initials: K
authors.lastname: Brixius
authors.forename: Annette
authors.initials: A
authors.lastname: Wollmer
authors.forename: Birgit
authors.initials: B
authors.lastname: Bölck
authors.forename: Uwe
authors.initials: U
authors.lastname: Mehlhorn
authors.forename: Robert H G
authors.initials: RH
authors.lastname: Schwinger
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000328:Adult; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002303:Cardiac Output, Low / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D002311:Cardiomyopathy, Dilated / Q000150:complications; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000235:genetics*; D009206:Myocardium / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D012694:Serine; D013912:Threonine; D000099211:Phospholamban
chemical_list: D000318:Adrenergic beta-Agonists; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D007527:Isoenzymes; D007545:Isoproterenol; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D012694:Serine; D013912:Threonine; D000099211:Phospholamban