scholarly journals Effect of rigor and cycling cross-bridges on the structure of troponin C and on the Ca2+ affinity of the Ca2+-specific regulatory sites in skinned rabbit psoas fibers.

1987 ◽  
Vol 262 (28) ◽  
pp. 13627-13635
Author(s):  
K Güth ◽  
J D Potter
Keyword(s):  
Troponin C ◽  
Rabbit Psoas ◽  
Cross Bridges ◽  
Regulatory Sites

Force, length, and Ca(2+)-troponin C affinity in skeletal muscle

1991 ◽  
Vol 261 (5) ◽  
pp. C787-C792 ◽  
Author(s):  
F. Fuchs ◽  
Y. P. Wang
Keyword(s):  
Skeletal Muscle ◽  
Protein Interactions ◽  
Muscle Fibers ◽  
Psoas Muscle ◽  
Troponin C ◽  
Force Generation ◽  
Fluorescence Probes ◽  
Protein Protein Interactions ◽  
Rabbit Psoas ◽  
Cross Bridges

On the basis of isotopic methods it has been found that force generation promotes increased Ca2+ binding to troponin C in cardiac muscle [P. Hofmann and F. Fuchs. Am. J. Physiol. 253 (Cell Physiol. 22): C541-C546, 1987] but not in skeletal muscle (J. Muscle Res. Cell Motil. 6: 477, 1985). However, studies with skinned rabbit psoas muscle fibers containing substituted fluorescent troponin C analogues indicate that force-generating cross bridges do promote increased Ca2+ binding in skeletal muscle (K. Guth and J. D. Potter. J. Biol. Chem. 262: 13627-13635, 1987). We have reexamined this question using a modified contraction-relaxation protocol in which Ca2+ binding to detergent-treated rabbit psoas fibers was measured either during steady-state force development or after relaxation was induced by one of two myosin ATPase inhibitors, vanadate or 2,3-butanedione monoxime. A standard double-isotope technique was used to measure Ca2+ binding. Another set of experiments was done in which force was reduced by releasing muscle fibers from sarcomere lengths of 2.4-2.6 microns to 1.5-1.7 microns, and bound Ca2+ was determined either before or after the release. No statistically significant effect of force generation or sarcomere length on Ca(2+)-troponin C affinity was observed. Thus the discrepancy remains between results obtained with isotopic and fluorescence methods. It is possible that in skinned fibers emission from fluorescence probes is more closely related to protein-protein interactions than to the amount of Ca2+ bound to troponin C.

scholarly journals Troponin C modulates the activation of thin filaments by rigor cross-bridges

1997 ◽  
Vol 72 (5) ◽  
pp. 2262-2267 ◽  
Author(s):  
P.W. Brandt ◽  
F.H. Schachat
Keyword(s):  
Troponin C ◽  
Thin Filaments ◽  
Cross Bridges

Functional and evolutionary relationships of troponin C

2007 ◽  
Vol 32 (1) ◽  
pp. 16-27 ◽  
Author(s):  
Todd E. Gillis ◽  
Christian R. Marshall ◽  
Glen F. Tibbits
Keyword(s):  
Functional Properties ◽  
Thin Filament ◽  
Troponin I ◽  
Striated Muscle ◽  
Troponin T ◽  
Extensive Study ◽  
Troponin C ◽  
High Conservation ◽  
Cross Bridges ◽  
And Function

Striated muscle contraction is initiated when, following membrane depolarization, Ca2+ binds to the low-affinity Ca2+ binding sites of troponin C (TnC). The Ca2+ activation of this protein results in a rearrangement of the components (troponin I, troponin T, and tropomyosin) of the thin filament, resulting in increased interaction between actin and myosin and the formation of cross bridges. The functional properties of this protein are therefore critical in determining the active properties of striated muscle. To date there are 61 known TnCs that have been cloned from 41 vertebrate and invertebrate species. In vertebrate species there are also distinct fast skeletal muscle and cardiac TnC proteins. While there is relatively high conservation of the amino acid sequence of TnC homologs between species and tissue types, there is wide variation in the functional properties of these proteins. To date there has been extensive study of the structure and function of this protein and how differences in these translate into the functional properties of muscles. The purpose of this work is to integrate these studies of TnC with phylogenetic analysis to investigate how changes in the sequence and function of this protein, integrate with the evolution of striated muscle.

The off rate of Ca2+ from troponin C is regulated by force-generating cross bridges in skeletal muscle

2002 ◽  
Vol 92 (6) ◽  
pp. 2409-2418 ◽  
Author(s):  
Ying Wang ◽  
W. Glenn L. Kerrick
Keyword(s):  
Skeletal Muscle ◽  
Troponin C ◽  
Transient Increase ◽  
Skinned Fibers ◽  
Mouse Skeletal Muscle ◽  
Actomyosin Atpase ◽  
Intact Muscle ◽  
Intracellular Ca ◽  
Cross Bridges ◽  
Fenn Effect

The effects of dissociation of force-generating cross bridges on intracellular Ca2+, pCa-force, and pCa-ATPase relationships were investigated in mouse skeletal muscle. Mechanical length perturbations were used to dissociate force-generating cross bridges in either intact or skinned fibers. In intact muscle, an impulse stretch or release, a continuous length vibration, a nonoverlap stretch, or an unloaded shortening during a twitch caused a transient increase in intracellular Ca2+ compared with that in isometric controls and resulted in deactivation of the muscle. In skinned fibers, sinusoidal length vibrations shifted pCa-force and pCa-actomyosin ATPase rate relationships to higher Ca2+ concentrations and caused actomyosin ATPase rate to decrease at submaximal Ca2+ and increase at maximal Ca2+ activation. These results suggest that dissociation of force-generating cross bridges during a twitch causes the off rate of Ca2+ from troponin C to increase (a decrease in the Ca2+ affinity of troponin C), thus decreasing the Ca2+ sensitivity and resulting in the deactivation of the muscle. The results also suggest that the Fenn effect only exists at maximal but not submaximal force-activating Ca2+ concentrations.

Coupling calcium binding to troponin C and cross-bridge cycling in skinned cardiac cells

1994 ◽  
Vol 266 (3) ◽  
pp. H1260-H1271 ◽  
Author(s):  
A. Landesberg ◽  
S. Sideman
Keyword(s):  
Cardiac Muscle ◽  
Calcium Binding ◽  
Troponin C ◽  
Cardiac Cells ◽  
Loose Coupling ◽  
Cross Bridge ◽  
Length Relationship ◽  
Troponin Complex ◽  
Cross Bridges

This study examines the coupling of calcium binding to troponin with the force developed by the cross bridges in the skinned cardiac muscle. It emphasizes the key role of the troponin complex in regulating cross-bridge cycling and defines four distinct states of the troponin complex in the single-overlap region. These include a "loose-coupling" state, wherein cross bridges can exist in the strong conformation without having calcium bound to the neighbor troponin C. Published simultaneous measurements of the force and the bound calcium are used to calculate the apparent calcium binding coefficients. The force-length relationships at different free calcium concentrations are used to evaluate the cooperative mechanism. The dependence of the affinity of troponin for calcium on the number of force-generating cross bridges is the dominant cooperative mechanism. The proposed loose-coupling model, with a positive feedback of force on calcium binding, describes the role of calcium in force regulation and the force-length relationship in skinned cardiac muscle. The ability to simulate the rate of force development is demonstrated.

scholarly journals X-ray diffraction studies of cross-bridges weakly bound to actin in relaxed skinned fibers of rabbit psoas muscle

1997 ◽  
Vol 73 (5) ◽  
pp. 2292-2303 ◽  
Author(s):  
S. Xu ◽  
S. Malinchik ◽  
D. Gilroy ◽  
T. Kraft ◽  
B. Brenner ◽  
...  
Keyword(s):  
Psoas Muscle ◽  
Skinned Fibers ◽  
X Ray Diffraction ◽  
Weakly Bound ◽  
X Ray ◽  
Rabbit Psoas ◽  
Cross Bridges

BDM affects nucleotide binding and force generation steps of the cross-bridge cycle in rabbit psoas muscle fibers

1994 ◽  
Vol 266 (2) ◽  
pp. C437-C447 ◽  
Author(s):  
Y. Zhao ◽  
M. Kawai
Keyword(s):  
Equilibrium Constants ◽  
Muscle Fibers ◽  
Psoas Muscle ◽  
Isometric Tension ◽  
Activation Mechanism ◽  
Phosphate Binding ◽  
Rabbit Psoas ◽  
Cross Bridge ◽  
The Cross ◽  
Cross Bridges

The effect of 2,3-butanedione monoxime (BDM) on elementary steps of the cross-bridge cycle was studied with the sinusoidal analysis technique in skinned rabbit psoas muscle fibers. Our results showed that isometric tension and stiffness decreased progressively with an increase in the BDM concentration. The MgATP and MgADP binding constants increased 27 and 6 times, respectively, when BDM was increased from 0 to 18 mM, whereas the phosphate binding constant did not change significantly. The equilibrium constants of the ATP isomerization and detachment step were not sensitive to BDM, whereas the equilibrium constant of the attachment (power stroke) step decreased with BDM. Thus, in the presence of BDM, the number of attached cross bridges decreases; more cross bridges accumulate in the detached state, causing isometric tension and stiffness to decline. However, our detailed analysis shows that the decrease in the number of attached cross bridges is approximately 40%, which is not adequate to account for the 84% decrease in the isometric tension when 18 mM BDM was present. Therefore we suggest that a thin-filament activation mechanism is also affected by BDM.

Dynamic relations among length, tension, and intracellular Ca2+ in activated ferret papillary muscles

1998 ◽  
Vol 275 (6) ◽  
pp. H1957-H1962 ◽  
Author(s):  
Yasutake Saeki ◽  
Satoshi Kurihara ◽  
Kimiaki Komukai ◽  
Tetsuya Ishikawa ◽  
Kiyohiro Takigiku
Keyword(s):  
Cardiac Troponin ◽  
Muscle Length ◽  
Length Change ◽  
Troponin C ◽  
Cardiac Troponin C ◽  
Mechanical Constraints ◽  
Tension Response ◽  
Cardiac Muscles ◽  
Length Changes ◽  
Cross Bridges

To study the effects of mechanical constraints on the Ca2+ affinity of cardiac troponin C, we analyzed the tension and aequorin light (AL) responses to sinusoidal length changes (5–10% of the initial muscle length) in aequorin-injected, tetanized cardiac muscles. The amplitude of the quasi-sinusoidal tension and AL responses decreased with increasing length-perturbation frequency from 0.5 to 1 Hz at 24°C and from 1 to 3 Hz at 30°C. The increase in AL corresponded well to the decrease in tension; likewise, the decrease in AL to the increase in tension and the tension response lagged behind the length change. A further increase in frequency (>1 Hz at 24°C and >3 Hz at 30°C) markedly increased the amplitude of the tension responses but decreased the amplitude of the AL responses. The increase in AL lagged behind the decrease in tension; likewise, the decrease in AL lagged behind the increase in tension, and the tension response led the length change. From previous mechanistic interpretations of the frequency dependence of the amplitude of tension response, we argue that the Ca2+affinity of cardiac troponin C changes in parallel with the active tension (i.e., the number of active cross bridges) but not with the passive tension produced by the length perturbation-induced cross-bridge strain.

scholarly journals Effects of troponin C isoform on the action of the cardiotonic agent EMD 57033

2005 ◽  
Vol 388 (3) ◽  
pp. 905-912 ◽  
Author(s):  
Simon LIPSCOMB ◽  
Laura C. PRESTON ◽  
Paul ROBINSON ◽  
Charles S. REDWOOD ◽  
Ian. P. MULLIGAN ◽  
...  
Keyword(s):  
Dynamic Stiffness ◽  
Troponin C ◽  
Rabbit Psoas ◽  
Relaxing Solution ◽  
Leftward Shift ◽  
Cardiotonic Agent ◽  
Tension Recovery ◽  
Tension Curve ◽  
Degree Of Extraction ◽  
Quantitative Response

The effects of the cardiotonic potentiator EMD 57033 on different TnC (troponin C) isoforms were investigated. Endogenous skeletal TnC was extracted from glycerinated, permeabilized rabbit psoas fibres and replaced with either purified native rabbit psoas TnC (fast TnC) or human recombinant cTnC (cardiac TnC) (3 mg/ml in relaxing solution for 30 min). In both conditions, 10 μM EMD 57033 increased maximal calcium-activated force (Pmax) and gave a leftward shift in the pCa–tension curve. With cTnC, the increase in Pmax was much greater (228%) compared with the effect seen for fast TnC (137%), which was the same as that in unextracted control fibres. When the whole troponin was replaced rather than just TnC, the effects of EMD 57033 on fibres replaced with cTn were the same as with the cTnC subunit alone, except that the force at low Ca2+ concentrations was not increased as much. If TnC was only partially extracted, it was found that the degree of extraction did not influence the effect of EMD 57033, except when force was decreased to below 10% of the pre-extraction Pmax. Dynamic stiffness was not altered by EMD 57033 in any of the preparations. The rate of tension recovery following a release–restretch method (ktr) was decreased by EMD 57033. We conclude that EMD 57033 acts by a rate-modulating effect, and that the quantitative response of this effect is dependent on the TnC isoform present.

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