title: Cardiac myosin-binding protein C is required for complete relaxation in intact myocytes.
abstract: The role of cardiac myosin-binding protein C (cMyBP-C) in cardiac contraction is still not fully resolved. Experimental ablation of cMyBP-C by various means resulted in inconsistent changes in Ca2+ sensitivity and increased velocity of force of skinned preparations. To evaluate how these effects are integrated in an intact, living myocyte context, we investigated consequences of cMyBP-C ablation in ventricular myocytes and left atria from cMyBP-C knock-out (KO) mice compared with wild-type (WT). At 6 weeks, KO myocytes exhibited mild hypertrophy that became more pronounced by 30 weeks. Isolated cells from KO exhibited markedly lower diastolic sarcomere length (SL) without change in diastolic Ca2+. The lower SL in KO was partly abolished by the actin-myosin ATPase inhibitors 2,3-butanedione monoxime or blebbistatin, indicating residual actin-myosin interaction in diastole. The relationship between cytosolic Ca2+ and SL showed that KO cells started to contract at lower Ca2+ without reaching a higher maximum, yielding a smaller area of the phase-plane diagram. Both sarcomere shortening and Ca2+ transient were prolonged in KO. Isolated KO left atria exhibited a marked increase in sensitivity to external Ca2+ and, in contrast to WT, continued to develop twitch force at low micromolar Ca2+. Taken together, the main consequence of cMyBP-C ablation was a defect in diastolic relaxation and a smaller dynamic range of cell shortening, both of which likely result from the increased myofilament Ca2+ sensitivity. Our findings indicate that cMyBP-C functions as a restraint on myosin-actin interaction at low Ca2+ and short SL to allow complete relaxation during diastole.
authors.affiliation: Institute of Experimental and Clinical Pharmacology and Toxicology, University Medical Center Hamburg-Eppendorf, D-20246 Hamburg, Germany.
authors.forename: Lutz
authors.initials: L
authors.lastname: Pohlmann
authors.forename: Irena
authors.initials: I
authors.lastname: Kröger
authors.forename: Nicolas
authors.initials: N
authors.lastname: Vignier
authors.forename: Saskia
authors.initials: S
authors.lastname: Schlossarek
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Krämer
authors.forename: Catherine
authors.initials: C
authors.lastname: Coirault
authors.forename: Karim R
authors.initials: KR
authors.lastname: Sultan
authors.forename: Ali
authors.initials: A
authors.lastname: El-Armouche
authors.forename: Saul
authors.initials: S
authors.lastname: Winegrad
authors.forename: Thomas
authors.initials: T
authors.lastname: Eschenhagen
authors.forename: Lucie
authors.initials: L
authors.lastname: Carrier
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D024741:Cardiomyopathy, Hypertrophic, Familial / Q000473:pathology / Q000503:physiopathology*; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism; D003971:Diastole / Q000502:physiology*; D006325:Heart Atria / Q000166:cytology; D051379:Mice; D018345:Mice, Knockout; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000473:pathology / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000378:metabolism; D010641:Phenotype; D012518:Sarcomeres / Q000502:physiology; D013599:Systole / Q000502:physiology; D000099163:Myosin Binding Protein C