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Nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers

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...

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Autores principales: Kawai, Masataka, Karam, Tarek S., Kolb, Justin, Wang, Li, Granzier, Henk L.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Rockefeller University Press 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6219688/
https://www.ncbi.nlm.nih.gov/pubmed/30301869
http://dx.doi.org/10.1085/jgp.201812104
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author Kawai, Masataka
Karam, Tarek S.
Kolb, Justin
Wang, Li
Granzier, Henk L.
author_facet Kawai, Masataka
Karam, Tarek S.
Kolb, Justin
Wang, Li
Granzier, Henk L.
author_sort Kawai, Masataka
collection PubMed
description 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(2+) 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 (K(2)), its rate (k(2)), and the rate of the reverse force generation step (k(−4)) are larger in Neb(+) fibers than in Neb(−) fibers. The rates of the force generation step (k(4)) and the reversal detachment step (k(−2)) 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.
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spelling pubmed-62196882019-05-05 Nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers Kawai, Masataka Karam, Tarek S. Kolb, Justin Wang, Li Granzier, Henk L. J Gen Physiol Research Articles 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(2+) 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 (K(2)), its rate (k(2)), and the rate of the reverse force generation step (k(−4)) are larger in Neb(+) fibers than in Neb(−) fibers. The rates of the force generation step (k(4)) and the reversal detachment step (k(−2)) 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. Rockefeller University Press 2018-11-05 /pmc/articles/PMC6219688/ /pubmed/30301869 http://dx.doi.org/10.1085/jgp.201812104 Text en © 2018 Kawai et al. http://www.rupress.org/terms/https://creativecommons.org/licenses/by-nc-sa/4.0/This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms/). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 International license, as described at https://creativecommons.org/licenses/by-nc-sa/4.0/).
spellingShingle Research Articles
Kawai, Masataka
Karam, Tarek S.
Kolb, Justin
Wang, Li
Granzier, Henk L.
Nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers
title Nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers
title_full Nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers
title_fullStr Nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers
title_full_unstemmed Nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers
title_short Nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers
title_sort nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers
topic Research Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6219688/
https://www.ncbi.nlm.nih.gov/pubmed/30301869
http://dx.doi.org/10.1085/jgp.201812104
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