Prevention of Myofilament Dysfunction by beta-Blocker Therapy in Postinfarct Remodeling

Background-Myofilament contractility of individual cardiomyocytes is depressed in remote noninfarcted myocardium and contributes to global left ventricular pump dysfunction after myocardial infarction (MI). Here, we investigated whether beta-blocker therapy could restore myofilament contractility. Methods and Results-In pigs with a MI induced by ligation of the left circumflex coronary artery, beta-blocker therapy (bisoprolol, MI+beta) was initiated on the first day after MI. Remote left ventricular subendocardial biopsies were taken 3 weeks after sham or MI surgery. Isometric force was measured in single permeabilized cardiomyocytes. Maximal force (F-max) was lower, whereas Ca2+ sensitivity was higher in untreated MI compared with sham (both P<0.05). The difference in Ca2+ sensitivity was abolished by treatment of cells with the beta-adrenergic kinase, protein kinase A. beta-blocker therapy partially reversed F-max and Ca2+ sensitivity to sham values and significantly reduced passive force. Despite the lower myofilament Ca2+ sensitivity in MI+beta compared with untreated myocardium, the protein kinase A induced reduction in Ca2+ sensitivity was largest in cardiomyocytes from myocardium treated with beta-blockers. Phosphorylation of beta-adrenergic target proteins (myosin binding protein C and troponin I) did not differ among groups, whereas myosin light chain 2 phosphorylation was reduced in MI, which coincided with increased expression of protein phosphatase 1. beta-blockade fully restored the latter alterations and significantly reduced expression of protein phosphatase 2a. Conclusions-beta-blockade reversed myofilament dysfunction and enhanced myofilament responsiveness to protein kinase A in remote myocardium after MI. These effects likely contribute to the beneficial effects of beta-blockade on global left ventricular function after MI. (Circ Heart Fail. 2009;2:233-242.)