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 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.

Fundamental step size in single cardiac and skeletal sarcomeres

2002 ◽  
Vol 283 (3) ◽  
pp. C735-C742 ◽  
Author(s):  
Olga Yakovenko ◽  
Felix Blyakhman ◽  
Gerald H. Pollack
Keyword(s):  
Actin Filaments ◽  
Thin Filament ◽  
Time Course ◽  
Flight Muscle ◽  
Length Change ◽  
Step Size ◽  
Fundamental Step ◽  
Dynamic Events ◽  
Photodiode Array ◽  
Parallel Measurements

In attempting to deduce the size of the elementary molecular translation step, recent experiments using single myosin molecules translating over actin filaments have shown a consistent step size of 5.4 nm (10, 21). We have carried out parallel measurements on single myofibrils from rabbit cardiac muscle and bumblebee flight muscle. Activated specimens were released or stretched with a motor-imposed ramp, and the time course of length of individual sarcomeres was measured by projecting the image of the striations onto a linear photodiode array and tracking the spacing between A-band centroids. We confirmed the 5.4-nm step. With subnanometer precision, however, we find that this value is two times that of a more fundamental step size of 2.7 nm. Step sizes were always integer multiples of 2.7 nm, whether the length change was positive or negative. This value is equal to the linear repeat of actin monomers along the thin filament, a result that ties dynamic events to molecular structure and places narrow constraints on any proposed molecular mechanism.

scholarly journals Kettin, a major source of myofibrillar stiffness in Drosophila indirect flight muscle

2001 ◽  
Vol 154 (5) ◽  
pp. 1045-1058 ◽  
Author(s):  
Michael Kulke ◽  
Ciprian Neagoe ◽  
Bernhard Kolmerer ◽  
Ave Minajeva ◽  
Horst Hinssen ◽  
...  
Keyword(s):  
Flight Muscle ◽  
Staining Pattern ◽  
Thick Filament ◽  
Indirect Flight Muscle ◽  
Similar Degree ◽  
Stretch Activation ◽  
Passive Stiffness ◽  
Force Measurements ◽  
Insect Muscle ◽  
Elastic Filament

Kettin is a high molecular mass protein of insect muscle that in the sarcomeres binds to actin and α-actinin. To investigate kettin's functional role, we combined immunolabeling experiments with mechanical and biochemical studies on indirect flight muscle (IFM) myofibrils of Drosophila melanogaster. Micrographs of stretched IFM sarcomeres labeled with kettin antibodies revealed staining of the Z-disc periphery. After extraction of the kettin-associated actin, the A-band edges were also stained. In contrast, the staining pattern of projectin, another IFM–I-band protein, was not altered by actin removal. Force measurements were performed on single IFM myofibrils to establish the passive length-tension relationship and record passive stiffness. Stiffness decreased within seconds during gelsolin incubation and to a similar degree upon kettin digestion with μ-calpain. Immunoblotting demonstrated the presence of kettin isoforms in normal Drosophila IFM myofibrils and in myofibrils from an actin-null mutant. Dotblot analysis revealed binding of COOH-terminal kettin domains to myosin. We conclude that kettin is attached not only to actin but also to the end of the thick filament. Kettin along with projectin may constitute the elastic filament system of insect IFM and determine the muscle's high stiffness necessary for stretch activation. Possibly, the two proteins modulate myofibrillar stiffness by expressing different size isoforms.

The Croonian Lecture, 1977 - Stretch activation of muscle: function and mechanism

1978 ◽  
Vol 201 (1143) ◽  
pp. 107-130 ◽  
Keyword(s):  
Skeletal Muscle ◽  
Heart Muscle ◽  
Flight Muscle ◽  
Mechanical Activity ◽  
Myosin Filament ◽  
Active Tension ◽  
Stretch Activation ◽  
Mammalian Heart ◽  
Mammalian Heart Muscle ◽  
Vertebrate Skeletal Muscle

Current theories about the mechanism of muscular contraction suppose that the level of enzymic and contractile activity is controlled by the intracellular concentration of calcium ions, the degree of overlap between the myosin and actin filaments and the rate of relative sliding of the filaments. It is now known that in most or all muscles there is a further direct influence of mechanical conditions, usually called stretch activation; changes of length lead to a delayed change of active tension. The effect is large and functionally significant in insect fibrillar flight muscle and in mammalian heart muscle; it is present, but small, in vertebrate skeletal muscle, which probably accounts for its late discovery. In insect fibrillar flight muscle, the delayed tension is responsible for the rhythmic mechanical activity during flight. In mammalian heart muscle it may play a rôle in Starling’s Law. In insect fibrillar muscle, extension produces a maintained increase in actomyosin ATPase and active tension; in vertebrate skeletal muscle, stretch activation is a transient phenomenon. Mammalian heart muscle shows greater maintenance of stretch activation than skeletal muscle; the duration of higher ATPase activity has not yet been determined. The effective mechanical parameter is not overall strain but is probably the strain on an internal structure related to overall stress. Various lines of evidence point to the myosin filament as the location of the sensor. A considerable degree of molecular synchronization occurs during natural insect flight.

Shortening deactivation: quantifying a critical component of cyclical muscle contraction

2021 ◽  
Author(s):  
Amy K. Loya ◽  
Sarah K. Van Houten ◽  
Bernadette M. Glasheen ◽  
Douglas M. Swank
Keyword(s):  
Power Output ◽  
Muscle Activation ◽  
Muscle Relaxation ◽  
Length Change ◽  
Isometric Tension ◽  
Energetic Cost ◽  
Muscle Shortening ◽  
Shortening Deactivation ◽  
Muscle Types ◽  
Flight Muscles

A muscle undergoing cyclical contractions requires fast and efficient muscle activation and relaxation to generate high power with relatively low energetic cost. To enhance activation and increase force levels during shortening, some muscle types have evolved stretch activation (SA), a delayed increased in force following rapid muscle lengthening. SA's complementary phenomenon is shortening deactivation (SD), a delayed decrease in force following muscle shortening. SD increases muscle relaxation, which decreases resistance to subsequent muscle lengthening. While it might be just as important to cyclical power output, SD has received less investigation than SA. To enable mechanistic investigations into SD and quantitatively compare it to SA, we developed a protocol to elicit SA and SD from Drosophila and Lethocerus indirect flight muscles (IFM) and Drosophila jump muscle. When normalized to isometric tension, Drosophila IFM exhibited a 118% SD tension decrease, Lethocerus IFM dropped by 97%, and Drosophila jump muscle decreased by 37%. The same order was found for normalized SA tension: Drosophila IFM increased by 233%, Lethocerus IFM by 76%, and Drosophila jump muscle by only 11%. SD occurred slightly earlier than SA, relative to the respective length change, for both IFMs; but SD was exceedingly earlier than SA for jump muscle. Our results suggest SA and SD evolved to enable highly efficient IFM cyclical power generation and may be caused by the same mechanism. However, jump muscle SA and SD mechanisms are likely different, and may have evolved for a role other than to increase the power output of cyclical contractions.

scholarly journals "Creep currents" in single frog atrial cells may be generated by electrogenic Na/Ca exchange.

1986 ◽  
Vol 87 (6) ◽  
pp. 857-884 ◽  
Author(s):  
J R Hume ◽  
A Uehara
Keyword(s):  
Voltage Clamp ◽  
Time Course ◽  
Single Cells ◽  
Mechanical Activity ◽  
Common Mechanism ◽  
Mechanical Relaxation ◽  
Equilibrium Conditions ◽  
Atrial Cells ◽  
Current Voltage ◽  
Wide Range

The objective of these experiments was to test the hypothesis that the "creep currents" induced by Na loading of single frog atrial cells (Hume, J. R., and A. Uehara. 1986. Journal of General Physiology. 87:833) may be generated by an electrogenic Na/Ca exchanger. Creep currents induced by Na loading were examined over a wide range of membrane potentials. During depolarizing voltage-clamp pulses, outward creep currents were observed, followed by inward creep currents upon the return to the holding potential. During hyperpolarizing voltage-clamp pulses, creep currents of the opposite polarity were observed: inward creep currents were observed during the pulses, followed by outward creep currents upon the return to the holding potential. The current-voltage relations for inward and outward creep currents in response to depolarizing or hyperpolarizing voltage displacements away from the holding potential all intersect the voltage axis at a common potential, which indicates that inward and outward creep currents may have a common reversal potential under equilibrium conditions and may therefore be generated by a common mechanism. Measurements of inward creep currents confirm that voltage displacements away from the holding potential rapidly alter equilibrium conditions. Current-voltage relationships of inward creep currents after depolarizing voltage-clamp pulses are extremely labile and depend critically upon the amplitude and duration of outward creep currents elicited during preceding voltage-clamp pulses. An optical monitor of mechanical activity in single cells revealed (a) a similar voltage dependence for the outward creep currents induced by Na loading and tonic contraction, and (b) a close correlation between the time course of the decay of the inward creep current and the time course of mechanical relaxation. A mathematical model of electrogenic Na/Ca exchange (Mullins, L.J. 1979. Federation Proceedings. 35:2583; Noble, D. 1986. Cardiac Muscle. 171-200) can adequately account for many of the properties of creep currents. It is concluded that creep currents in single frog atrial cells may be attributed to the operation of an electrogenic Na/Ca exchange mechanism.

Parietal Area 5 Activity Does Not Reflect the Differential Time-Course of Motor Output Kinetics During Arm-Reaching and Isometric-Force Tasks

2006 ◽  
Vol 95 (6) ◽  
pp. 3353-3370 ◽  
Author(s):  
Catherine Hamel-Pâquet ◽  
Lauren E. Sergio ◽  
John F. Kalaska
Keyword(s):  
Time Course ◽  
Posterior Parietal Cortex ◽  
Primary Motor Cortex ◽  
Isometric Force ◽  
Arm Movement ◽  
Population Level ◽  
Motor Output ◽  
Initial Increase ◽  
Related Area ◽  
Area 5

Many single-neuron recording studies have examined the degree to which the activity of primary motor cortex (M1) neurons is related to the kinematics and kinetics of various motor tasks. This has not been explored as extensively for arm movement-related neurons in posterior parietal cortex area 5. We recorded the activity of 78 proximal arm–related neurons in area 5 of two monkeys while they used their whole arm to make reaching movements toward eight targets on a horizontal plane against an inertial load or to generate isometric forces at the hand in the same eight horizontal directions. The overall range of measured output forces was similar in the two tasks. The forces increased monotonically in the desired direction in the isometric task. In the movement task, in contrast, they showed a rapid initial increase in the direction of movement, followed by a transient reversal of forces as the hand approached the target. Many task-related area 5 neurons were tuned for the direction of motor output in the tasks, but most area 5 neurons were more strongly active or exclusively active in the movement task than in the isometric task. Furthermore, their activity at either the single cell or population level did not reflect the transient reversal of output forces during movement. In contrast, M1 neuronal activity was typically strong in both tasks and showed task-related changes that reflected the differences in the time course and directionality of force outputs between both tasks, including the transient reversal of forces in the movement task. These results show that area 5 neurons are less strongly related to the time-course of task kinetics than M1 during isometric and arm-movement tasks.

scholarly journals Prolonged cross-bridge binding triggers muscle dysfunction in a Drosophila model of myosin-based hypertrophic cardiomyopathy

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
William A Kronert ◽  
Kaylyn M Bell ◽  
Meera C Viswanathan ◽  
Girish C Melkani ◽  
Adriana S Trujillo ◽  
...  
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Flight Muscle ◽  
Isometric Force ◽  
Muscle Mechanics ◽  
Muscle Dysfunction ◽  
Cardiac Myosin ◽  
Cross Bridge ◽  
Drosophila Model ◽  
Mechanistic Basis ◽  
Tension Generation

K146N is a dominant mutation in human β-cardiac myosin heavy chain, which causes hypertrophic cardiomyopathy. We examined how Drosophila muscle responds to this mutation and integratively analyzed the biochemical, physiological and mechanical foundations of the disease. ATPase assays, actin motility, and indirect flight muscle mechanics suggest at least two rate constants of the cross-bridge cycle are altered by the mutation: increased myosin attachment to actin and decreased detachment, yielding prolonged binding. This increases isometric force generation, but also resistive force and work absorption during cyclical contractions, resulting in decreased work, power output, flight ability and degeneration of flight muscle sarcomere morphology. Consistent with prolonged cross-bridge binding serving as the mechanistic basis of the disease and with human phenotypes, 146N/+ hearts are hypercontractile with increased tension generation periods, decreased diastolic/systolic diameters and myofibrillar disarray. This suggests that screening mutated Drosophila hearts could rapidly identify hypertrophic cardiomyopathy alleles and treatments.

The α7β1-integrin accelerates fiber hypertrophy and myogenesis following a single bout of eccentric exercise

2011 ◽  
Vol 301 (4) ◽  
pp. C938-C946 ◽  
Author(s):  
Tara N. Lueders ◽  
Kai Zou ◽  
Heather D. Huntsman ◽  
Benjamin Meador ◽  
Ziad Mahmassani ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Eccentric Exercise ◽  
Time Course ◽  
Muscle Hypertrophy ◽  
Isometric Force ◽  
Transmembrane Protein ◽  
Mechanical Strain ◽  
Cellular Growth ◽  
Cross Sectional ◽  
Single Bout

The α7β1-integrin is a heterodimeric transmembrane protein that adheres to laminin in the extracellular matrix, representing a critical link that maintains structure in skeletal muscle. In addition to preventing exercise-induced skeletal muscle injury, the α7-integrin has been proposed to act as an intrinsic mechanosensor, initiating cellular growth in response to mechanical strain. The purpose of this study was to determine the extent to which the α7-integrin regulates muscle hypertrophy following eccentric exercise. Wild-type (WT) and α7-integrin transgenic (α7Tg) mice completed a single bout of downhill running exercise (−20°, 17 m/min, 60 min), and gastrocnemius-soleus complexes were collected 1, 2, 4, and 7 days (D) postexercise (PE). Maximal isometric force was maintained and macrophage accumulation was suppressed in α7Tg muscle 1D PE. Mean fiber cross-sectional area was unaltered in WT mice but increased 40% in α7Tg mice 7D PE. In addition, a rapid and striking fivefold increase in embryonic myosin heavy chain-positive fibers appeared in α7Tg mice 2D PE. Although Pax7-positive satellite cells were increased in α7Tg muscle 1D PE, the number of nuclei per myofiber was not altered 7D PE. Phosphorylation of mammalian target of rapamycin (mTOR) was significantly elevated in α7Tg 1D PE. This study provides the first demonstration that the presence of the α7β1-integrin in skeletal muscle increases fiber hypertrophy and new fiber synthesis in the early time course following a single bout of eccentric exercise. Further studies are necessary to elucidate the precise mechanism by which the α7-integrin can enhance muscle hypertrophy following exercise.

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