Role of cardiac myosin binding protein C in sustaining left ventricular systolic stiffening.
Despite advances in the molecular biology of cardiac myosin binding protein-C (cMyBP-C), little is understood about its precise role in muscle contraction, particularly in the intact heart. We tested the hypothesis that cMyBP-C is central to the time course and magnitude of left ventricular systolic elastance (chamber stiffening), and assessed mechanisms for this influence in intact hearts, trabeculae, and skinned fibers from wild-type (+/+) and homozygous truncated cMyBP-C (t/t) male mice. cMyBP-C protein was not detected by gel electrophoresis or Western blot in t/t myocardium. cMyBP-C t/t ventricles displayed reduced peak elastance, but more strikingly a marked abbreviation of the systolic elastance time course, which peaked earlier (27.6+/-2.1 ms) than in +/+ controls (47.8+/-1.6 ms). Control hearts reached only 42+/-4% of maximum elastance at the onset of ejection, with substantial further stiffening during ejection. This contrasted to t/t mutants, which reached 77+/-3% of peak elastance before ejection of peak. These unusual findings were not observed in alternative models involving severe cardiomyopathy, but were recapitulated in a cMyBP-C null mouse. The abbreviated elastance time course and lower peak were consistent with earlier time-to-peak trabecular tension, increased unloaded shortening velocity in t/t skinned muscle strips, and dramatically reduced myofilament stiffness at diastolic calcium concentrations. These results provide novel insights into the role of cMyBP-C in myocardial systolic mechanics. Abnormal sarcomere shortening velocity and abbreviated muscle stiffening may underlie development of cardiac dysfunction associated with deficient incorporation of cMyBP-C.
Palmer
Bradley M
BM
Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA. palmer@physiology.med.uvm.edu
Georgakopoulos
Dimitrios
D
Janssen
Paul M
PM
Wang
Yuan
Y
Alpert
Norman R
NR
Belardi
Diego F
DF
Harris
Samantha P
SP
Moss
Richard L
RL
Burgon
Patrick G
PG
Seidman
Christine E
CE
Seidman
J G
JG
Maughan
David W
DW
Kass
David A
DA
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D004548:Elasticity; D005260:Female; D005838:Genotype; D006352:Heart Ventricles / Q000737:chemistry / Q000648:ultrastructure*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009200:Myocardial Contraction / Q000235:genetics / Q000502:physiology*; D012518:Sarcomeres / Q000737:chemistry / Q000502:physiology*; D013329:Structure-Activity Relationship; D013599:Systole / Q000502:physiology*; D013997:Time Factors; D016277:Ventricular Function, Left / Q000235:genetics / Q000502:physiology*; D014783:Viscosity; D000099163:Myosin Binding Protein C
D002352:Carrier Proteins; D000099163:Myosin Binding Protein C