scholarly journals Kinetics of a Ca(2+)-sensitive cross-bridge state transition in skeletal muscle fibers. Effects due to variations in thin filament activation by extraction of troponin C.

1991 ◽  
Vol 98 (2) ◽  
pp. 233-248 ◽  
Author(s):  
J M Metzger ◽  
R L Moss
Keyword(s):  
Steady State ◽  
Direct Effect ◽  
Thin Filament ◽  
Near Neighbor ◽  
Troponin C ◽  
Isometric Tension ◽  
Cross Bridge ◽  
Filament Activation ◽  
Kinetics Of ◽  
Partial Extraction

The rate constant of tension redevelopment (ktr; 1986. Proc. Natl. Acad. Sci. USA. 83:3542-3546) was determined at various levels of thin filament activation in skinned single fibers from mammalian fast twitch muscles. Activation was altered by (a) varying the concentration of free Ca2+ in the activating solution, or (b) extracting various amounts of troponin C (TnC) from whole troponin complexes while keeping the concentration of Ca2+ constant. TnC was extracted by bathing the fiber in a solution containing 5 mM EDTA, 10 mM HEPES, and 0.5 mM trifluoperazine dihydrochloride. Partial extraction of TnC resulted in a decrease in the Ca2+ sensitivity of isometric tension, presumably due to disruption of near-neighbor molecular cooperativity between functional groups (i.e., seven actin monomers plus associated troponin and tropomyosin) within the thin filament. Altering the level of thin filament activation by partial extraction of TnC while keeping Ca2+ concentration constant tested whether the Ca2+ sensitivity of ktr results from a direct effect of Ca2+ on cross-bridge state transitions or, alternatively, an indirect effect of Ca2+ on these transitions due to varying extents of thin filament activation. Results showed that the ktr-pCa relation was unaffected by partial extraction of TnC, while steady-state isometric tension exhibited the expected reduction in Ca2+ sensitivity. This finding provides evidence for a direct effect of Ca2+ on an apparent rate constant that limits the formation of force-bearing cross-bridge states in muscle fibers. Further, the kinetics of this transition are unaffected by disruption of near-neighbor thin filament cooperativity subsequent to extraction of TnC. Finally, the results support the idea that the steepness of the steady-state isometric tension-calcium relationship is at least in part due to mechanisms involving molecular cooperativity among thin filament regulatory proteins.

scholarly journals Kinetics of Cardiac Thin-Filament Activation Probed by Fluorescence Polarization of Rhodamine-Labeled Troponin C in Skinned Guinea Pig Trabeculae

2006 ◽  
Vol 90 (2) ◽  
pp. 531-543 ◽  
Author(s):  
Marcus G. Bell ◽  
Edward B. Lankford ◽  
Gregory E. Gonye ◽  
Graham C.R. Ellis-Davies ◽  
Donald A. Martyn ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Fluorescence Polarization ◽  
Thin Filament ◽  
Troponin C ◽  
Filament Activation ◽  
Kinetics Of

scholarly journals The effects of partial extraction of TnC upon the tension-pCa relationship in rabbit skinned skeletal muscle fibers.

1985 ◽  
Vol 86 (4) ◽  
pp. 585-600 ◽  
Author(s):  
R L Moss ◽  
G G Giulian ◽  
M L Greaser
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Polyacrylamide Gel Electrophoresis ◽  
Regulatory Protein ◽  
Sodium Dodecyl ◽  
Isometric Tension ◽  
Original Position ◽  
Experimental Chamber ◽  
Psoas Muscles ◽  
Partial Extraction

The activation of contraction in vertebrate skeletal muscle involves the binding of Ca2+ to low-affinity binding sites on the troponin C (TnC) subunit of the regulatory protein troponin. The present study is an investigation of possible cooperative interactions between adjacent functional groups, composed of seven actin monomers, one tropomyosin, and one troponin, along the same thin filament. Single skinned fibers were obtained from rabbit psoas muscles and were then placed in an experimental chamber containing relaxing solution maintained at 15 degrees C. Isometric tension was measured in solutions containing maximally and submaximally activating levels of free Ca2+ (a) in control fiber segments, (b) in the same segments after partial extraction of TnC, and finally (c) after recombination of TnC into the segments. The extraction was done at 11-13 degrees C in 20 mM Tris, 5 mM EDTA, pH 7.85 or 8.3, a procedure derived from that of Cox et al. (1981. Biochem. J. 195:205). Extraction of TnC was quantitated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the control and experimental samples. Partial extraction of TnC resulted in reductions in tension during maximal Ca activation and in a shift of the relative tension-pCa (i.e., -log[Ca2+]) relationship to lower pCa's. The readdition of TnC to the extracted fiber segments resulted in a recovery of tension to near-control levels and in the return of the tension-pCa relation to its original position. On the basis of these findings, we conclude that the sensitivity to Ca2+ of a functional group within the thin filament may vary depending upon the state of activation of immediately adjacent groups.

Myosin MgADP release rate decreases at longer sarcomere length to prolong myosin attachment time in skinned rat myocardium

2015 ◽  
Vol 309 (12) ◽  
pp. H2087-H2097 ◽  
Author(s):  
Bertrand C. W. Tanner ◽  
Jason J. Breithaupt ◽  
Peter O. Awinda
Keyword(s):  
Release Rate ◽  
Thin Filament ◽  
Molecular Mechanisms ◽  
Sarcomere Length ◽  
Cardiac Contractility ◽  
Force Production ◽  
Cross Bridge ◽  
Thin Filament Proteins ◽  
Filament Activation ◽  
Ventricular Filling

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.

Calcium removal kinetics of the sarcoplasmic reticulum ATPase in skeletal muscle

1997 ◽  
Vol 272 (4) ◽  
pp. C1087-C1098 ◽  
Author(s):  
E. E. Burmeister Getz ◽  
S. L. Lehman
Keyword(s):  
Skeletal Muscle ◽  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
Initial Rate ◽  
Troponin C ◽  
The Other ◽  
Physiological Conditions ◽  
Initial Binding ◽  
Kinetics Of ◽  
Transient And Steady State

The models of the sarcoplasmic reticulum (SR) Ca pump used to simulate Ca kinetics in muscle fibers are simple but inconsistent with data on Ca binding or steady-state uptake. We develop a model of the SR pump that is consistent with data on transient and steady-state Ca removal and has rate constants identified under near-physiological conditions. We also develop models of the other main Ca-binding proteins in skeletal muscle: troponin C and parvalbumin. These models are used to simulate Ca transients in cut fibers during and after depolarizing pulses. Simulations using the full SR pump model are contrasted with simulations using a Michaelis-Menten (MM) approximation to SR pump kinetics. The MM pump underestimates the amount of Ca released during depolarization, underestimates the initial rate of Ca binding by the pump, and overestimates the later rate of Ca pumping. These errors are due to fast initial binding by the SR pump, which is neglected in the MM approximation.

scholarly journals Nebulin Alters Cross-bridge Cycling Kinetics and Increases Thin Filament Activation

2009 ◽  
Vol 284 (45) ◽  
pp. 30889-30896 ◽  
Author(s):  
Murali Chandra ◽  
Ranganath Mamidi ◽  
Steven Ford ◽  
Carlos Hidalgo ◽  
Christian Witt ◽  
...  
Keyword(s):  
Thin Filament ◽  
Cross Bridge ◽  
Filament Activation
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