Actomyosin interactions in cMYBP-C−/− mice
The precise role of cardiac myosin binding protein C (cMyBP-C) on contractility and on actomyosin interaction (AMI) remains unknown. We hypothesized that the lack of cMyBP-C impaired cardiac AMI. Mechanical properties and AMI characteristics in left papillary muscle and the in vitro motility of actin filaments on purified myosin molecules were performed from 16-weeks old cMyBP-C−/−KO and WT (n = 16 in both groups). Compared to WT, both total tension and maximum shortening velocity were lower in KO (p < 0.001). The probability of cross-bridge attachment was higher in KO than in WT (8.6 ± 0.3 vs. 5.4 ± 0.2%, p < 0.05). The number of active AIM was lower in KO (6.4 ± 0.9 vs. 11.6 ± 1.0 109/mm2, p < 0.001) as well as the unitary force per AIM (p < 0.01). Power stroke probability was reduced in KO compared to WT (5.0 ± 0.4 vs. 8.1 ± 0.4%, p < 0.05). Myosin-based velocities of actin were slower in KO than in WT (1.65 ± 0.01 vs. 1.98 ± 0.01 μm/s, p < 0.01). These data suggest that cMyBP-C regulates AIM by limiting inefficient cross-bridge formation and by enhancing the power stroke step.