Effect of cardiac myosin binding protein-C on mechanoenergetics in mouse myocardium.
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.
Palmer
Bradley M
BM
Department of Molecular Physiology and Biophysics, University of Vermont College of Medicine, University of Vermont, Burlington, Vt 05405, USA. palmer@physiology.med.uvm.edu
Noguchi
Teruo
T
Wang
Yuan
Y
Heim
John R
JR
Alpert
Norman R
NR
Burgon
Patrick G
PG
Seidman
Christine E
CE
Seidman
J G
JG
Maughan
David W
DW
LeWinter
Martin M
MM
D008841:Actin Cytoskeleton / Q000502:physiology / Q000648:ultrastructure; D000205:Actomyosin / Q000502:physiology; D000818:Animals; D001696:Biomechanical Phenomena; D020013:Calcium Signaling; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D004548:Elasticity; D004734:Energy Metabolism; D005260:Female; D007537:Isometric Contraction; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009200:Myocardial Contraction / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000502:physiology; D010101:Oxygen Consumption; D010710:Phosphates / Q000502:physiology; D011441:Propylthiouracil / Q000633:toxicity; D013599:Systole; D016276:Ventricular Function; D014783:Viscosity; D000099163:Myosin Binding Protein C
D000205:Actomyosin; D002352:Carrier Proteins; D018995:Myosin Heavy Chains; D010710:Phosphates; D011441:Propylthiouracil; D000099163:Myosin Binding Protein C