scholarly journals Mechanical transients initiated by photolysis of caged ATP within fibers of insect fibrillar flight muscle.

1991 ◽  
Vol 98 (4) ◽  
pp. 657-679 ◽  
Author(s):  
M Yamakawa ◽  
Y E Goldman
Keyword(s):  
Rate Constant ◽  
Time Course ◽  
Flight Muscle ◽  
Order Rate Constant ◽  
Stretch Activation ◽  
Pulse Photolysis ◽  
Caged Atp ◽  
Cross Bridge ◽  
The Cross ◽  
Cross Bridges

Kinetics of the cross-bridge cycle in insect fibrillar flight muscle have been measured using laser pulse photolysis of caged ATP and caged inorganic phosphate (Pi) to produce rapid step increases in the concentration of ATP and Pi within single glycerol-extracted fibers. Rapid photochemical liberation of 100 microM-1 mM ATP from caged ATP within a fiber caused relaxation in the absence of Ca2+ and initiated an active contraction in the presence of approximately 30 microM Ca2+. The apparent second order rate constant for detachment of rigor cross-bridges by ATP was between 5 x 10(4) and 2 x 10(5) M-1s-1. This rate is not appreciably sensitive to the Ca2+ or Pi concentrations or to rigor tension level. The value is within an order of magnitude of the analogous reaction rate constant measured with isolated actin and insect myosin subfragment-1 (1986. J. Muscle Res. Cell Motil. 7:179-192). In both the absence and presence of Ca2+ insect fibers showed evidence of transient cross-bridge reattachment after ATP-induced detachment from rigor, as found in corresponding experiments on rabbit psoas fibers. However, in contrast to results with rabbit fibers, tension traces of insect fibers starting at different rigor tensions did not converge to a common time course until late in the transients. This result suggests that the proportion of myosin cross-bridges that can reattach into force-generating states depends on stress or strain in the filament lattice. A steady 10-mM concentration of Pi markedly decreased the transient reattachment phase after caged ATP photolysis. Pi also decreased the amplitude of stretch activation after step stretches applied in the presence of Ca2+ and ATP. Photolysis of caged Pi during stretch activation abruptly terminated the development of tension. These results are consistent with a linkage between Pi release and the steps leading to force production in the cross-bridge cycle.

scholarly journals Phosphate binding induced force-reversal occurs via slow backward cycling of cross-bridges

2020 ◽  
Author(s):  
R Stehle
Keyword(s):  
Rate Constant ◽  
Force Generation ◽  
Phosphate Binding ◽  
Reversible Process ◽  
Cross Bridge ◽  
Force Relation ◽  
The Cross ◽  
Cross Bridges ◽  
Bridge Models ◽  
Kinetics Of

ABSTRACTThe release of inorganic phosphate (Pi) from the cross-bridge is a pivotal step in the cross-bridge ATPase cycle leading to force generation. It is well known that Pi release and the force-generating step are reversible, thus increase of [Pi] decreases isometric force by product inhibition and increases the rate constant kTR of mechanically-induced force redevelopment due to the reversible redistribution of cross-bridges among non-force-generating and force-generating states. The experiments on cardiac myofibrils from guinea pig presented here show that increasing [Pi] increases kTR almost reciprocally to force, i.e., kTR ≈ 1/force. To elucidate which cross-bridge models can explain the reciprocal kTR-force relation, simulations were performed for models varying in sequence and kinetics of 1) the Pi release-rebinding equilibrium, 2) the force-generating step and its reversal, and 3) the transitions limiting forward and backward cycling of cross-bridges between non-force-generating and force-generating states. Models consisting of fast reversible force generation before/after rapid Pi release-rebinding fail to describe the kTR–force relation observed in experiments. Models consistent with the experimental kTR-force relation have in common that Pi binding and/or force-reversal are/is intrinsically slow, i.e., either Pi binding or force-reversal or both limit backward cycling of cross-bridges from force-generating to non-force-generating states.STATEMENT OF SIGNIFICANCEPrevious mechanical studies on muscle fibers, myofibrils and myosin interacting with actin revealed that force production associated to phosphate release from myosin’s active site presents a reversible process in the cross-bridge cycle. The correlation of this reversible process to the process(es) limiting kinetics of backward cycling from force-generating to non-force-generating states remained unclear.Experimental data of cardiac myofibrils and model simulations show that the combined effects of [Pi] on force and the rate constant of force redevelopment (kTR) are inconsistent with fast reversible force generation before/after rapid Pi release-rebinding. The minimum requirement in sequential models for successfully describing the experimentally observed nearly reciprocal change of force and kTR is that either the Pi binding or the force-reversal step limit backward cycling.

Cooperative attachment of cross bridges predicts regulation of smooth muscle force by myosin phosphorylation

2004 ◽  
Vol 287 (3) ◽  
pp. C594-C602 ◽  
Author(s):  
Christopher M. Rembold ◽  
Robert L. Wardle ◽  
Christopher J. Wingard ◽  
Timothy W. Batts ◽  
Elaine F. Etter ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Smooth Muscle ◽  
Time Course ◽  
Muscle Force ◽  
Regulatory System ◽  
Force Development ◽  
Cross Bridge ◽  
Cross Bridges ◽  
The Relationship ◽  
Cooperative Activation

Serine 19 phosphorylation of the myosin regulatory light chain (MRLC) appears to be the primary determinant of smooth muscle force development. The relationship between MRLC phosphorylation and force is nonlinear, showing that phosphorylation is not a simple switch regulating the number of cycling cross bridges. We reexamined the MRLC phosphorylation-force relationship in slow, tonic swine carotid media; fast, phasic rabbit urinary bladder detrusor; and very fast, tonic rat anococcygeus. We found a sigmoidal dependence of force on MRLC phosphorylation in all three tissues with a threshold for force development of ∼0.15 mol Pi/mol MRLC. This behavior suggests that force is regulated in a highly cooperative manner. We then determined whether a model that employs both the latch-bridge hypothesis and cooperative activation could reproduce the relationship between Ser19-MRLC phosphorylation and force without the need for a second regulatory system. We based this model on skeletal muscle in which attached cross bridges cooperatively activate thin filaments to facilitate cross-bridge attachment. We found that such a model describes both the steady-state and time-course relationship between Ser19-MRLC phosphorylation and force. The model required both cooperative activation and latch-bridge formation to predict force. The best fit of the model occurred when binding of a cross bridge cooperatively activated seven myosin binding sites on the thin filament. This result suggests cooperative mechanisms analogous to skeletal muscle that will require testing.

Asynchronous muscle: a primer

2000 ◽  
Vol 203 (18) ◽  
pp. 2713-2722 ◽  
Author(s):  
R.K. Josephson ◽  
J.G. Malamud ◽  
D.R. Stokes
Keyword(s):  
Time Course ◽  
Flight Muscle ◽  
Isometric Force ◽  
Length Change ◽  
Mechanical Activity ◽  
Stretch Activation ◽  
Passive Stiffness ◽  
Schistocerca Americana ◽  
Slow Time ◽  
Shortening Deactivation

The asynchronous muscles of insects are characterized by asynchrony between muscle electrical and mechanical activity, a fibrillar organization with poorly developed sarcoplasmic reticulum, a slow time course of isometric contraction, low isometric force, high passive stiffness and delayed stretch activation and shortening deactivation. These properties are illustrated by comparing an asynchronous muscle, the basalar flight muscle of the beetle Cotinus mutabilis, with synchronous wing muscles from the locust, Schistocerca americana. Because of delayed stretch activation and shortening deactivation, a tetanically stimulated beetle muscle can do work when subjected to repetitive lengthening and shortening. The synchronous locust muscle, subjected to similar stimulation and length change, absorbs rather than produces work.

scholarly journals FmhA and FmhC of Staphylococcus aureus incorporate serine residues into peptidoglycan cross-bridges

2020 ◽  
Vol 295 (39) ◽  
pp. 13664-13676 ◽  
Author(s):  
Stephanie Willing ◽  
Emma Dyer ◽  
Olaf Schneewind ◽  
Dominique Missiakas
Keyword(s):  
Staphylococcus Aureus ◽  
Cell Wall ◽  
Binding Proteins ◽  
Penicillin Binding Proteins ◽  
Daughter Cells ◽  
Cross Bridge ◽  
Resistant Strains ◽  
The Cross ◽  
Cross Bridges ◽  
Adjacent Wall

Staphylococcal peptidoglycan is characterized by pentaglycine cross-bridges that are cross-linked between adjacent wall peptides by penicillin-binding proteins to confer robustness and flexibility. In Staphylococcus aureus, pentaglycine cross-bridges are synthesized by three proteins: FemX adds the first glycine, and the homodimers FemA and FemB sequentially add two Gly-Gly dipeptides. Occasionally, serine residues are also incorporated into the cross-bridges by enzymes that have heretofore not been identified. Here, we show that the FemA/FemB homologues FmhA and FmhC pair with FemA and FemB to incorporate Gly-Ser dipeptides into cross-bridges and to confer resistance to lysostaphin, a secreted bacteriocin that cleaves the pentaglycine cross-bridge. FmhA incorporates serine residues at positions 3 and 5 of the cross-bridge. In contrast, FmhC incorporates a single serine at position 5. Serine incorporation also lowers resistance toward oxacillin, an antibiotic that targets penicillin-binding proteins, in both methicillin-sensitive and methicillin-resistant strains of S. aureus. FmhC is encoded by a gene immediately adjacent to lytN, which specifies a hydrolase that cleaves the bond between the fifth glycine of cross-bridges and the alanine of the adjacent stem peptide. In this manner, LytN facilitates the separation of daughter cells. Cell wall damage induced upon lytN overexpression can be alleviated by overexpression of fmhC. Together, these observations suggest that FmhA and FmhC generate peptidoglycan cross-bridges with unique serine patterns that provide protection from endogenous murein hydrolases governing cell division and from bacteriocins produced by microbial competitors.

scholarly journals Stretch of active muscle during the declining phase of the calcium transient produces biphasic changes in calcium binding to the activating sites.

1990 ◽  
Vol 96 (5) ◽  
pp. 1013-1035 ◽  
Author(s):  
A M Gordon ◽  
E B Ridgway
Keyword(s):  
Calcium Binding ◽  
Time Course ◽  
Control Level ◽  
Calcium Transient ◽  
Length Change ◽  
Positive Phase ◽  
Active Force ◽  
Cross Bridge ◽  
Calcium Affinity ◽  
Cross Bridges

In voltage-clamped barnacle single muscle fibers, muscle shortening during the declining phase of the calcium transient increases myoplasmic calcium. This extra calcium is probably released from the activating sites by a change in affinity when cross-bridges break (Gordon, A. M., and E. B. Ridgway, 1987. J. Gen. Physiol. 90:321-340). Stretching the muscle at similar times causes a more complex response, a rapid increase in intracellular calcium followed by a transient decrease. The amplitudes of both phases increase with the rate and amplitude of stretch. The rapid increase, however, appears only when the muscle is stretched more than approximately 0.4%. This is above the length change that produces the breakpoint in the force record during a ramp stretch. This positive phase in response to large stretches is similar to that seen on equivalent shortening at the same point in the contraction. For stretches at different times during the calcium transient, the peak amplitude of the positive phase has a time course that is delayed relative to the calcium transient, while the peak decrease during the negative phase has an earlier time course that is more similar to the calcium transient. The amplitudes of both phases increase with increasing strength of stimulation and consequent force. When the initial muscle the active force. A large decrease in length (which drops the active force to zero) decreases the extra calcium seen on a subsequent restretch. After such a shortening step, the extra calcium on stretch recovers (50 ms half time) toward the control level with the same time course as the redeveloped force. Conversely, stretching an active fiber decreases the extra calcium on a subsequent shortening step that is imposed shortly afterward. Enhanced calcium binding due to increased length alone cannot explain our data. We hypothesize that the calcium affinity of the activating sites increases with cross-bridge attachment and further with cross-bridge strain. This accounts for the biphasic response to stretch as follows: cross-bridges detached by stretch first decrease calcium affinity, then upon reattachment increase calcium affinity due to the strained configuration brought on by the stretch. The experiments suggest that cross-bridge attachment and strain can modify calcium binding to the activating sites in intact muscle.

scholarly journals Activation Dependence of Stretch Activation in Mouse Skinned Myocardium: Implications for Ventricular Function

2006 ◽  
Vol 127 (2) ◽  
pp. 95-107 ◽  
Author(s):  
Julian E. Stelzer ◽  
Lars Larsson ◽  
Daniel P. Fitzsimons ◽  
Richard L. Moss
Keyword(s):  
Isometric Force ◽  
Force Characteristic ◽  
Stretch Activation ◽  
Thin Filaments ◽  
Cross Bridge ◽  
Steady Level ◽  
Myocardial Stretch ◽  
Myosin Subfragment 1 ◽  
Activation Response ◽  
Cross Bridges

Recent evidence suggests that ventricular ejection is partly powered by a delayed development of force, i.e., stretch activation, in regions of the ventricular wall due to stretch resulting from torsional twist of the ventricle around the apex-to-base axis. Given the potential importance of stretch activation in cardiac function, we characterized the stretch activation response and its Ca2+ dependence in murine skinned myocardium at 22°C in solutions of varying Ca2+ concentrations. Stretch activation was induced by suddenly imposing a stretch of 0.5–2.5% of initial length to the isometrically contracting muscle and then holding the muscle at the new length. The force response to stretch was multiphasic: force initially increased in proportion to the amount of stretch, reached a peak, and then declined to a minimum before redeveloping to a new steady level. This last phase of the response is the delayed force characteristic of myocardial stretch activation and is presumably due to increased attachment of cross-bridges as a consequence of stretch. The amplitude and rate of stretch activation varied with Ca2+ concentration and more specifically with the level of isometric force prior to the stretch. Since myocardial force is regulated both by Ca2+ binding to troponin-C and cross-bridge binding to thin filaments, we explored the role of cross-bridge binding in the stretch activation response using NEM-S1, a strong-binding, non-force–generating derivative of myosin subfragment 1. NEM-S1 treatment at submaximal Ca2+-activated isometric forces significantly accelerated the rate of the stretch activation response and reduced its amplitude. These data show that the rate and amplitude of myocardial stretch activation vary with the level of activation and that stretch activation involves cooperative binding of cross-bridges to the thin filament. Such a mechanism would contribute to increased systolic ejection in response to increased delivery of activator Ca2+ during excitation–contraction coupling.

Non-cross-bridge calcium-dependent stiffness in frog muscle fibers

2004 ◽  
Vol 286 (6) ◽  
pp. C1353-C1357 ◽  
Author(s):  
M. A. Bagni ◽  
B. Colombini ◽  
P. Geiger ◽  
R. Berlinguer Palmini ◽  
G. Cecchi
Keyword(s):  
Time Course ◽  
Frog Muscle ◽  
Static Stiffness ◽  
Bridge Formation ◽  
Calcium Dependent ◽  
Cross Bridge ◽  
Steady Level ◽  
Intracellular Ca ◽  
Butanedione Monoxime ◽  
Cross Bridges

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.

scholarly journals Different structural states of a microtubule cross-linking molecule, captured by quick-freezing motile axostyles in protozoa.

1986 ◽  
Vol 103 (6) ◽  
pp. 2209-2227 ◽  
Author(s):  
J E Heuser
Keyword(s):  
Active Role ◽  
Longitudinal Shear ◽  
The Other ◽  
Cross Bridge ◽  
Other Hand ◽  
Quick Freezing ◽  
Cross Links ◽  
Dynein Arms ◽  
The Cross ◽  
Cross Bridges

Freeze-etch preparation of the laminated bundles of microtubules in motile axostyles demonstrates that the cross-bridges populating individual layers or laminae are structurally similar to the dynein arms of cilia and flagellae. Also, like dynein, they are extracted by high salt and undergo a change in tilt upon removal of endogenous ATP (while the axostyle as a whole straightens and becomes stiff). On the other hand, the bridges running between adjacent microtubule laminae in the axostyle turn out to be much more delicate and wispy in appearance, and display no similarity to dynein arms. Thus we propose that the internal or "intra-laminar" cross-bridges are the active force-generating ATPases in this system, and that they generate overall bends or changes in the helical pitch of the axostyle by altering the longitudinal and lateral register of microtubules in each lamina individually; e.g., by "warping" each lamina and creating longitudinal shear forces within it. The cross-links between adjacent laminae, on the other hand, would then simply be force-transmitting elements that serve to translate the shearing forces generated within individual laminae into overall helical shape changes. (This hypothesis differs from the views of earlier workers who considered a more active role for the later cross-links, postulating that they cause an active sliding between adjacent layers that somehow leads to axostyle movement.) Also described here are physical connections between adjacent intra-laminar cross-bridges, structurally analogous to the overlapping components of the outer dynein arms of cilia and flagella. As with dynein, these may represent a mechanism for propagating local changes from cross-bridge to cross-bridge down the axostyle, as occurs during the passage of bends down the length of the organelle.

scholarly journals Three-dimensional image reconstruction of insect flight muscle. I. The rigor myac layer.

1989 ◽  
Vol 109 (3) ◽  
pp. 1085-1102 ◽  
Author(s):  
K A Taylor ◽  
M C Reedy ◽  
L Córdova ◽  
M K Reedy
Keyword(s):  
Thin Filament ◽  
Flight Muscle ◽  
Insect Flight ◽  
Three Dimensional ◽  
Bridge Structure ◽  
Insect Flight Muscle ◽  
Single Filament ◽  
Cross Bridge ◽  
Cross Bridges

We have obtained detailed three-dimensional images of in situ cross-bridge structure in insect flight muscle by electron microscopy of multiple tilt views of single filament layers in ultrathin sections, supplemented with data from thick sections. In this report, we describe the images obtained of the myac layer, a 25-nm longitudinal section containing a single layer of alternating myosin and actin filaments. The reconstruction reveals averaged rigor cross-bridges that clearly separate into two classes constituting lead and rear chevrons within each 38.7-nm axial repeat. These two classes differ in tilt angle, size and shape, density, and slew. This new reconstruction confirms our earlier interpretation of the lead bridge as a two-headed cross-bridge and the rear bridge as a single-headed cross-bridge. The importance of complementing tilt series with additional projections outside the goniometer tilt range is demonstrated by comparison with our earlier myac layer reconstruction. Incorporation of this additional data reveals new details of rigor cross-bridge structure in situ which include clear delineation of (a) a triangular shape for the lead bridge, (b) a smaller size for the rear bridge, and (c) density continuity across the thin filament in the lead bridge. Within actin's regular 38.7-nm helical repeat, local twist variations in the thin filament that correlate with the two cross-bridge classes persist in this new reconstruction. These observations show that in situ rigor cross-bridges are not uniform, and suggest three different myosin head conformations in rigor.

scholarly journals Milrinone inhibits contractility in skinned skeletal muscle fibers

1998 ◽  
Vol 274 (5) ◽  
pp. C1306-C1311 ◽  
Author(s):  
C. Y. Seow ◽  
L. Morishita ◽  
B. H. Bressler
Keyword(s):  
Skeletal Muscle ◽  
Direct Action ◽  
Force Production ◽  
Isometric Tension ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Reduction In Force ◽  
Cross Bridge ◽  
The Cross ◽  
Cross Bridges

Direct action of the cardiotonic bipyridine milrinone on the cross bridges of single fibers of skinned rabbit skeletal muscle was investigated. At 10°C and pH 7.0, milrinone reduced isometric tension in a logarithmically concentration-dependent manner, with a 55% reduction in force at 0.6 mM. Milrinone also reduced Ca2+ sensitivity of skinned fibers in terms of force production; the shift in the force-pCa curve indicated a change in the pCa value at 50% maximal force from 6.10 to 5.94. The unloaded velocity of shortening was reduced by 18% in the presence of 0.6 mM milrinone. Parts of the transient tension response to step change in length were altered by milrinone, so that the test and control transients could not be superimposed. The results indicate that milrinone interferes with the cross-bridge cycle and possibly detains cross bridges in low-force states. The results also suggest that the positive inotropic effect of milrinone on cardiac muscle is probably not due to the drug’s direct action on the muscle cross bridges. The specific and reversible action of the bipyridine on muscle cross bridges makes it a potentially useful tool for probing the chemomechanical cross-bridge cycle.

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