Phosphorylation of C-protein, troponin I and phospholamban in isolated rabbit hearts.
Phosphorylation of myofibrillar and sacroplasmic-reticulum (SR) proteins was studied in Langendorff-perfused rabbit hearts subjected to various inotropic interventions. Stimulation of hearts with isoprenaline resulted in the phosphorylation of both troponin I (TnI) and C-protein in myofibrils and phospholamban in SR. Phosphorylation of phospholamban could be reversed by a 15 min perfusion with drug-free buffer, after a 1 minute pulse perfusion with isoprenaline, at which time the mechanical effects of isoprenaline stimulation had also been reversed. However, both TnI and C-protein remained phosphorylated at this time. Moreover, the inhibition of Ca2+ activation of the Mg2+-dependent ATPase (Mg-ATPase) activity associated with myofibrillar phosphorylation persisted in myofibrils prepared from hearts frozen after 15 min of washout of isoprenaline. To assess the contribution of C-protein phosphorylation in the decrease of Ca2+ activation of the myofibrillar Mg-ATPase activity, we reconstituted a regulated actomyosin system in which only C-protein was phosphorylated. In this system, C-protein phosphorylation did not contribute to the decrease in Ca2+ activation of Mg-ATPase activity, indicating that TnI phosphorylation is responsible for the diminished sensitivity of the myofibrils to Ca2+. These observations support the hypothesis that phospholamban phosphorylation plays a more dominant role than TnI or C-protein phosphorylation in the mechanical response of the mammalian heart to beta-adrenergic stimulation.
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009210:Myofibrils / Q000378:metabolism; D010766:Phosphorylation; D011817:Rabbits; D014336:Troponin / Q000378:metabolism*; D019210:Troponin I; D000099211:Phospholamban
D017301:Ca(2+) Mg(2+)-ATPase; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D005576:Colforsin; D000242:Cyclic AMP; D007545:Isoproterenol; D014336:Troponin; D019210:Troponin I; D000099211:Phospholamban; C020723:citrate-binding transport protein