Journal article
Nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers
The Journal of general physiology, Vol.150(11), pp.1510-1522
11/05/2018
DOI: 10.1085/jgp.201812104
PMCID: PMC6219688
PMID: 30301869
Abstract
Nebulin (Neb) is associated with the thin filament in skeletal muscle cells, but its functions are not well understood. For this goal, we study skinned slow-twitch soleus muscle fibers from wild-type (Neb
) and conditional Neb knockout (Neb
) mice. We characterize cross-bridge (CB) kinetics and the elementary steps of the CB cycle by sinusoidal analysis during full Ca
activation and observe that Neb increases active tension 1.9-fold, active stiffness 2.7-fold, and rigor stiffness 3.0-fold. The ratio of stiffness during activation and rigor states is 62% in Neb
fibers and 68% in Neb
fibers. These are approximately proportionate to the number of strongly attached CBs during activation. Because the thin filament length is 15% shorter in Neb
fibers than in Neb
fibers, the increase in force per CB in the presence of Neb is ∼1.5 fold. The equilibrium constant of the CB detachment step (
), its rate (
), and the rate of the reverse force generation step (
) are larger in Neb
fibers than in Neb
fibers. The rates of the force generation step (
) and the reversal detachment step (
) change in the opposite direction. These effects can be explained by Le Chatelier's principle: Increased CB strain promotes less force-generating state(s) and/or detached state(s). Further, when CB distributions among the six states are calculated, there is no significant difference in the number of strongly attached CBs between fibers with and without Neb. These results demonstrate that Neb increases force per CB. We also confirm that force is generated by isomerization of actomyosin (AM) from the AM.ADP.Pi state (ADP, adenosine diphophate; Pi, phosphate) to the AM*ADP.Pi state, where the same force is maintained after Pi release to result in the AM*ADP state. We propose that Neb changes the actin (and myosin) conformation for better ionic and hydrophobic/stereospecific AM interaction, and that the effect of Neb is similar to that of tropomyosin.
Details
- Title: Subtitle
- Nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers
- Creators
- Masataka Kawai - Departments of Anatomy and Cell Biology, and Internal Medicine, College of Medicine, University of Iowa, Iowa City, IA masataka-kawai@uiowa.eduTarek S Karam - Departments of Anatomy and Cell Biology, and Internal Medicine, College of Medicine, University of Iowa, Iowa City, IAJustin Kolb - Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZLi Wang - School of Nursing, Soochow University, Suzhou, ChinaHenk L Granzier - Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ
- Resource Type
- Journal article
- Publication Details
- The Journal of general physiology, Vol.150(11), pp.1510-1522
- DOI
- 10.1085/jgp.201812104
- PMID
- 30301869
- PMCID
- PMC6219688
- NLM abbreviation
- J Gen Physiol
- ISSN
- 0022-1295
- eISSN
- 1540-7748
- Publisher
- United States
- Grant note
- R01 AR053897 / NIAMS NIH HHS
- Language
- English
- Date published
- 11/05/2018
- Academic Unit
- Anatomy and Cell Biology; Internal Medicine
- Record Identifier
- 9984025415602771
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