Journal
BIOPHYSICAL JOURNAL
Volume 96, Issue 8, Pages 3273-3280Publisher
CELL PRESS
DOI: 10.1016/j.bpj.2008.12.3946
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Funding
- National Institutes of Health [HL59408]
- Nationa Science Foundation [MCB 0315865, IOB 0718417]
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Using atomic force microscopy, we examined the contribution of cardiac myosin binding protein-C (cMyBP-C) to thick-filament length and flexural rigidity. Native thick filaments were isolated from the hearts of transgenic mice bearing a truncation mutation of cMyBP-C (t/t) that results in no detectable cMyBP-C and from age-matched wild-type controls (+/+). Atomic force microscopy images of these filaments were evaluated with an automated analysis algorithm that identified filament position and shape. The t/t thick-filament length (1.48 +/- 0.02 mu m) was significantly (P < 0.01) shorter than +/+ (1.56 +/- 0.02 mu m). This 5%-shorter thick-filament length in the t/t was reflected in 4% significantly shorter sarcomere lengths of relaxed isolated cardiomyocytes of the t/t (1.97 +/- 0.01 mu m) compared to +/+ (2.05 +/- 0.01 mu m). To determine if cMyBP-C contributes to the mechanical properties of thick filaments, we used statistical polymer chain mechanics to calculate a per-filament-specific persistence length, an index of flexural rigidity directly proportional to Young's modulus. Thick-filament-specific persistence length in the t/t (373 +/- 62 mu m) was significantly lower than in +/+ (639 +/- 101 mu m). Accordingly, Young's modulus of t/t thick filaments was similar to 60% of +/+. These results provide what we consider a new understanding for the critical role of cMyBP-C in defining normal cardiac output by sustaining force and muscle stiffness.
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