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  • Title: Effect of cardiac myosin binding protein-C on mechanoenergetics in mouse myocardium.
    Author: Palmer BM, Noguchi T, Wang Y, Heim JR, Alpert NR, Burgon PG, Seidman CE, Seidman JG, Maughan DW, LeWinter MM.
    Journal: Circ Res; 2004 Jun 25; 94(12):1615-22. PubMed ID: 15155526.
    Abstract:
    We examined the effect of cardiac myosin binding protein-C (cMyBP-C) on contractile efficiency in isovolumically contracting left ventricle (LV) and on internal viscosity and oscillatory work production in skinned myocardial strips. A 6-week diet of 0.15% 6-n-propyl-2-thiouracil (PTU) was fed to wild-type (+/+(PTU)) and homozygous-truncated cMyBP-C (t/t(PTU)) mice starting at age approximately 8 weeks and leading to a myosin heavy chain (MHC) isoform profile of 10% alpha-MHC and 90% beta-MHC in both groups. Western blot analysis confirmed that cMyBP-C was present in the +/+(PTU) and effectively absent in the t/t(PTU). Total LV mechanical energy per beat was quantified as pressure-volume area (PVA). O2 consumption (Vo2) per beat was plotted against PVA at varying LV volumes. The reciprocal of the slope of the linear Vo2-PVA relation represents the contractile efficiency of converting O2 to mechanical energy. Contractile efficiency was significantly enhanced in t/t(PTU) (26.1+/-2.6%) compared with +/+(PTU) (17.1+/-1.6%). In skinned myocardial strips, maximum isometric tension was similar in t/t(PTU) (18.7+/-2.1 mN x mm(-2)) and +/+(PTU) (21.9+/-4.0 mN x mm(-2)), but maximum oscillatory work induced by sinusoidal length perturbations occurred at higher frequencies in t/t(PTU) (7.31+/-1.17 Hz) compared with +/+(PTU) (4.48+/-0.60 Hz) and was significantly more sensitive to phosphate concentration in the t/t(PTU). Under rigor conditions, the internal viscous load was significantly lower in the t/t(PTU) compared with +/+(PTU), ie, approximately 40% lower at 1 Hz. These results collectively suggest that contractile efficiency is enhanced in the t/t(PTU), probably through a reduced loss of mechanical energy by a viscous load normally provided by cMyBP-C and through a gain of phosphate-dependent oscillatory work normally inhibited by cMyBP-C.
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