Skeletal and cardiac α-actin isoforms differently modulate myosin cross-bridge formation and myofibre force production

2013 ◽  
Vol 22 (21) ◽  
pp. 4398-4404 ◽  
Author(s):  
Julien Ochala ◽  
Hiroyuki Iwamoto ◽  
Gianina Ravenscroft ◽  
Nigel G. Laing ◽  
Kristen J. Nowak
2008 ◽  
Vol 294 (1) ◽  
pp. C74-C78 ◽  
Author(s):  
V. Joumaa ◽  
D. E. Rassier ◽  
T. R. Leonard ◽  
W. Herzog

The aim of the present study was to test whether titin is a calcium-dependent spring and whether it is the source of the passive force enhancement observed in muscle and single fiber preparations. We measured passive force enhancement in troponin C (TnC)-depleted myofibrils in which active force production was completely eliminated. The TnC-depleted construct allowed for the investigation of the effect of calcium concentration on passive force, without the confounding effects of actin-myosin cross-bridge formation and active force production. Passive forces in TnC-depleted myofibrils ( n = 6) were 35.0 ± 2.9 nN/ μm2 when stretched to an average sarcomere length of 3.4 μm in a solution with low calcium concentration (pCa 8.0). Passive forces in the same myofibrils increased by 25% to 30% when stretches were performed in a solution with high calcium concentration (pCa 3.5). Since it is well accepted that titin is the primary source for passive force in rabbit psoas myofibrils and since the increase in passive force in TnC-depleted myofibrils was abolished after trypsin treatment, our results suggest that increasing calcium concentration is associated with increased titin stiffness. However, this calcium-induced titin stiffness accounted for only ∼25% of the passive force enhancement observed in intact myofibrils. Therefore, ∼75% of the normally occurring passive force enhancement remains unexplained. The findings of the present study suggest that passive force enhancement is partly caused by a calcium-induced increase in titin stiffness but also requires cross-bridge formation and/or active force production for full manifestation.


2013 ◽  
Vol 104 (2) ◽  
pp. 153a
Author(s):  
Rafael Shimkunas ◽  
Om Makwana ◽  
Mona Bazagan ◽  
Paul C. Simpson ◽  
Mark B. Ratcliffe ◽  
...  

1987 ◽  
Vol 65 (8) ◽  
pp. 1798-1801 ◽  
Author(s):  
J. M. Renaud ◽  
R. B. Stein ◽  
T. Gordon

Changes in force and stiffness during contractions of mouse extensor digitorum longus and soleus muscles were measured over a range of extracellular pH from 6.4 to 7.4. Muscle stiffness was measured using small amplitude (<0.1% of muscle length), high frequency (1.5 kHz) oscillations in length. Twitch force was not significantly affected by changes in pH, but the peak force during repetitive stimulation (2, 3, and 20 pulses) was decreased significantly as the pH was reduced. Changes in muscle stiffness with pH were in the same direction, but smaller in extent. If the number of attached cross-bridges in the muscle can be determined from the measurement of small amplitude, high frequency muscle stiffness, then these findings suggest that (a) the number of cross-bridges between thick and thin filaments declines in low pH and (b) the average force per cross-bridge also declines in low pH. The decline in force per cross-bridge could arise from a reduction in the ability of cross-bridges to generate force during their state of active force production and (or) in an increased percentage of bonds in a low force, "rigor" state.


2021 ◽  
Vol 129 (Suppl_1) ◽  
Author(s):  
Rohit Singh ◽  
Sakthivel Sadayappan

Rationale: Normal heart function depends on cardiac myosin binding protein-C (cMyBP-C) phosphorylation. Its decrease is associated with heart failure (HF) by inhibiting actomyosin interactions. In absence of cMyBP-C phosphorylation, the protein is bound to myosin S2, but released when phosphorylated, allowing myosin to form cross-bridges with actin. Challenging cMyBP-C/myosin S2 interaction by myopeptide (the first 126 amino acids of myosin S2) could promote actomyosin interaction in vitro , but its ability to improve contractility in HF remains untested. Objective: To test contractile function in skinned papillary fibers of a cMyBP-C dephosphorylated mouse model using myopeptide. Methods and Results: To mimic constitutive phosphoablation, a knock-in mouse model was established to express cMyBP-C in which serines 273, 282 and 302 were mutated to alanine (cMyBP-C AAA ). Western blotting revealed 50% and 100% of cMyBP-C AAA in het and homo mouse hearts, respectively. Echocardiography showed a decreased percentage of ejection fraction (28%, p<0.01) and fractional shortening (30%, p< 0.05) in both het and homo cMyBP-C AAA mice at 3 months of age, compared to knock-in negative controls. These mice also developed diastolic dysfunction with elevated ratio of E/A and E/e’ waves. Next, pCa-force measurements using skinned papillary fibers determined that maximal force (F max ) and rate of cross-bridge formation ( k tr ) were decreased in the cMyBP-C AAA groups, compared to the control. However, administration of dose-dependent myopeptide increased F max and k tr in wild-type and cMyBP-C AAA permeabilized skinned papillary fibers without affecting myofilament Ca 2+ sensitivity. Conclusions: Myopeptide can increase contractile force and rate of cross-bridge formation by releasing cMyBP-C/myosin S2 and promoting actomyosin formation of cross-bridges, thus validating its therapeutic potential.


2014 ◽  
Vol 307 (8) ◽  
pp. H1150-H1158 ◽  
Author(s):  
Rafael Shimkunas ◽  
Om Makwana ◽  
Kimberly Spaulding ◽  
Mona Bazargan ◽  
Michael Khazalpour ◽  
...  

After myocardial infarction, a poorly contracting nonischemic border zone forms adjacent to the infarct. The cause of border zone dysfunction is unclear. The goal of this study was to determine the myofilament mechanisms involved in postinfarction border zone dysfunction. Two weeks after anteroapical infarction of sheep hearts, we studied in vitro isometric and isotonic contractions of demembranated myocardium from the infarct border zone and a zone remote from the infarct. Maximal force development (Fmax) of the border zone myocardium was reduced by 31 ± 2% versus the remote zone myocardium ( n = 6/group, P < 0.0001). Decreased border zone Fmax was not due to a reduced content of contractile material, as assessed histologically, and from myosin content. Furthermore, decreased border zone Fmax did not involve altered cross-bridge kinetics, as assessed by muscle shortening velocity and force development kinetics. Decreased border zone Fmax was associated with decreased cross-bridge formation, as assessed from muscle stiffness in the absence of ATP where cross-bridge formation should be maximized (rigor stiffness was reduced 34 ± 6%, n = 5, P = 0.011 vs. the remote zone). Furthermore, the border zone myocardium had significantly reduced phosphorylation of myosin essential light chain (ELC; 41 ± 10%, n = 4, P < 0.05). However, for animals treated with doxycycline, an inhibitor of matrix metalloproteinases, rigor stiffness and ELC phosphorylation were not reduced in the border zone myocardium, suggesting that doxycycline had a protective effect. In conclusion, myofilament dysfunction contributes to postinfarction border zone dysfunction, myofilament dysfunction involves impaired cross-bridge formation and decreased ELC phosphorylation, and matrix metalloproteinase inhibition may be beneficial for limiting postinfarct border zone dysfunction.


2004 ◽  
Vol 286 (6) ◽  
pp. C1353-C1357 ◽  
Author(s):  
M. A. Bagni ◽  
B. Colombini ◽  
P. Geiger ◽  
R. Berlinguer Palmini ◽  
G. Cecchi

At the end of the force transient elicited by a fast stretch applied to an activated frog muscle fiber, the force settles to a steady level exceeding the isometric level preceding the stretch. We showed previously that this excess of tension, referred to as “static tension,” is due to the elongation of some elastic sarcomere structure, outside the cross bridges. The stiffness of this structure, “static stiffness,” increased upon stimulation following a time course well distinct from tension and roughly similar to intracellular Ca2+ concentration. In the experiments reported here, we investigated the possible role of Ca2+ in static stiffness by comparing static stiffness measurements in the presence of Ca2+ release inhibitors (D600, Dantrolene, 2H2O) and cross-bridge formation inhibitors [2,3-butanedione monoxime (BDM), hypertonicity]. Both series of agents inhibited tension; however, only D600, Dantrolene, and 2H2O decreased at the same time static stiffness, whereas BDM and hypertonicity left static stiffness unaltered. These results indicate that Ca2+, in addition to promoting cross-bridge formation, increases the stiffness of an (unidentified) elastic structure of the sarcomere. This stiffness increase may help in maintaining the sarcomere length uniformity under conditions of instability.


2015 ◽  
Vol 309 (12) ◽  
pp. H2087-H2097 ◽  
Author(s):  
Bertrand C. W. Tanner ◽  
Jason J. Breithaupt ◽  
Peter O. Awinda

Cardiac contractility increases as sarcomere length increases, suggesting that intrinsic molecular mechanisms underlie the Frank-Starling relationship to confer increased cardiac output with greater ventricular filling. The capacity of myosin to bind with actin and generate force in a muscle cell is Ca2+ regulated by thin-filament proteins and spatially regulated by sarcomere length as thick-to-thin filament overlap varies. One mechanism underlying greater cardiac contractility as sarcomere length increases could involve longer myosin attachment time ( t on) due to slowed myosin kinetics at longer sarcomere length. To test this idea, we used stochastic length-perturbation analysis in skinned rat papillary muscle strips to measure t on as [MgATP] varied (0.05–5 mM) at 1.9 and 2.2 μm sarcomere lengths. From this t on-MgATP relationship, we calculated cross-bridge MgADP release rate and MgATP binding rates. As MgATP increased, t on decreased for both sarcomere lengths, but t on was roughly 70% longer for 2.2 vs. 1.9 μm sarcomere length at maximally activated conditions. These t on differences were driven by a slower MgADP release rate at 2.2 μm sarcomere length (41 ± 3 vs. 74 ± 7 s−1), since MgATP binding rate was not different between the two sarcomere lengths. At submaximal activation levels near the pCa50 value of the tension-pCa relationship for each sarcomere length, length-dependent increases in t on were roughly 15% longer for 2.2 vs. 1.9 μm sarcomere length. These changes in cross-bridge kinetics could amplify cooperative cross-bridge contributions to force production and thin-filament activation at longer sarcomere length and suggest that length-dependent changes in myosin MgADP release rate may contribute to the Frank-Starling relationship in the heart.


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