Journal
BIOPHYSICAL JOURNAL
Volume 92, Issue 7, Pages 2476-2490Publisher
BIOPHYSICAL SOCIETY
DOI: 10.1529/biophysj.106.099549
Keywords
-
Categories
Funding
- NIAMS NIH HHS [R01 AR049033, R01AR049033-03] Funding Source: Medline
Ask authors/readers for more resources
The stiffness of the single myosin motor ( e) is determined in skinned fibers from rabbit psoas muscle by both mechanical and thermodynamic approaches. Changes in the elastic strain of the half-sarcomere ( hs) are measured by fast mechanics both in rigor, when all myosin heads are attached, and during active contraction, with the isometric force ( T-0) modulated by changing either [ Ca2+] or temperature. The hs compliance is 43.0 +/- 0.8 nm MPa-1 in isometric contraction at saturating [ Ca2+], whereas in rigor it is 28.2 +/- 1.1 nm MPa-1. The equivalent compliance of myofilaments is 21.0 +/- 3.3 nm MPa-1. Accordingly, the stiffness of the ensemble of myosin heads attached in the hs is 45.5 +/- 1.7 kPa nm(-1) in isometric contraction at saturating [ Ca2+] ( e(0)), and in rigor ( er) it rises to 138.9 +/- 21.2 kPa nm(-1). e, calculated from er and the lattice molecular dimensions, is 1.21 +/- 0.18 pN nm(-1). e estimated, using a thermodynamic approach, from the relation of T-0 at saturating [ Ca2+] versus the reciprocal of absolute temperature is 1.25 +/- 0.14 pN nm(-1), similar to that estimated for. bers in rigor. Consequently, the ratio e(0)/e(r) ( 0.33 +/- 0.05) can be used to estimate the fraction of attached heads during isometric contraction at saturating [ Ca2+]. If the osmotic agent dextran T-500 ( 4 g/100 ml) is used to reduce the lateral. lament spacing of the relaxed fiber to the value before skinning, both e(0) and er increase by; 40%. e becomes; 1.7 pN nm(-1) and the fraction and the force of myosin heads attached in the isometric contraction remain the same as before dextran application. The finding that the fraction of myosin heads attached to actin in an isometric contraction is 0.33 rules out the hypothesis of multiple mechanical cycles per ATP hydrolyzed.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available