scholarly journals High ionic strength and low pH detain activated skinned rabbit skeletal muscle crossbridges in a low force state.

1993 ◽  
Vol 101 (4) ◽  
pp. 487-511 ◽  
Author(s):  
C Y Seow ◽  
L E Ford
Keyword(s):  
Skeletal Muscle ◽  
Ionic Strength ◽  
Isometric Force ◽  
Maximum Velocity ◽  
Low Ph ◽  
High Ionic Strength ◽  
Rabbit Skeletal Muscle ◽  
Shortening Velocity ◽  
Force Ratio ◽  
Force Difference

The effects of varying pH and ionic strength on the force-velocity relations and tension transients of skinned rabbit skeletal muscle were studied at 1-2 degrees C. Both decreasing pH from 7.35 to 6.35 and raising ionic strength from 125 to 360 mM reduced isometric force by about half and decreased sarcomere stiffness by about one-fourth, so that the stiffness/force ratio was increased by half. Lowering pH also decreased maximum shortening velocity by approximately 29%, while increasing ionic strength had little effect on velocity. These effects on velocity were correlated with asymmetrical effects on stiffness. The increase in the stiffness/force ratio with both interventions was manifest as a greater relative force change associated with a sarcomere length step. This force difference persisted for a variable time after the step. At the high ionic strength the force difference was long-lasting after stretches but relaxed quickly after releases, suggesting that the structures responsible would not impose much resistance to steady-state shortening. The opposite was found in the low pH experiments. The force difference relaxed quickly after stretches but persisted for a long time after releases. Furthermore, this force difference reached a constant value of approximately 8% of isometric force with intermediate sizes of release, and was not increased with larger releases. This value was almost identical to the value of an internal load that would be sufficient to account for the reduction in maximum velocity seen at the low pH. The results are interpreted as showing that both low pH and high ionic strength inhibit the movement of crossbridges into the force-generating parts of their cycle after they have attached to the actin filaments, with very few other effects on the cycle. The two interventions are different, however, in that detained bridges can be detached readily by shortening when the detention is caused by high ionic strength but not when it is caused by low pH.

scholarly journals Active shortening protects against stretch-induced force deficits in human skeletal muscle

2017 ◽  
Vol 122 (5) ◽  
pp. 1218-1226 ◽  
Author(s):  
Anjali L. Saripalli ◽  
Kristoffer B. Sugg ◽  
Christopher L. Mendias ◽  
Susan V. Brooks ◽  
Dennis R. Claflin
Keyword(s):  
Skeletal Muscle ◽  
High Velocity ◽  
Isometric Force ◽  
Human Subjects ◽  
Causative Factor ◽  
Negative Consequences ◽  
Shortening Velocity ◽  
Contracting Muscle ◽  
Working Hypothesis ◽  
Force Maintenance

Skeletal muscle contraction results from molecular interactions of myosin “crossbridges” with adjacent actin filament binding sites. The binding of myosin to actin can be “weak” or “strong,” and only strong binding states contribute to force production. During active shortening, the number of strongly bound crossbridges declines with increasing shortening velocity. Forcibly stretching a muscle that is actively shortening at high velocity results in no apparent negative consequences, whereas stretch of an isometrically (fixed-length) contracting muscle causes ultrastructural damage and a decline in force-generating capability. Our working hypothesis is that stretch-induced damage is uniquely attributable to the population of crossbridges that are strongly bound. We tested the hypothesis that stretch-induced force deficits decline as the prevailing shortening velocity is increased. Experiments were performed on permeabilized segments of individual skeletal muscle fibers obtained from human subjects. Fibers were maximally activated and allowed either to generate maximum isometric force (Fo), or to shorten at velocities that resulted in force maintenance of ≈50% Fo or ≈2% Fo. For each test condition, a rapid stretch equivalent to 0.1 × optimal fiber length was applied. Relative to prestretch Fo, force deficits resulting from stretches applied during force maintenance of 100, ≈50, and ≈2% Fo were 23.2 ± 8.6, 7.8 ± 4.2, and 0.3 ± 3.3%, respectively (means ± SD, n = 20). We conclude that stretch-induced damage declines with increasing shortening velocity, consistent with the working hypothesis that the fraction of strongly bound crossbridges is a causative factor in the susceptibility of skeletal muscle to stretch-induced damage. NEW & NOTEWORTHY Force deficits caused by stretch of contracting muscle are most severe when the stretch is applied during an isometric contraction, but prevented if the muscle is shortening at high velocity when the stretch occurs. This study indicates that velocity-controlled modulation of the number of strongly bound crossbridges is the basis for the observed relationship between stretch-induced muscle damage and prevailing shortening velocity.

scholarly journals A 72,000-mol-wt protein from tomato inhibits rabbit acto-S-1 ATPase activity.

1983 ◽  
Vol 96 (6) ◽  
pp. 1761-1765 ◽  
Author(s):  
M Vahey
Keyword(s):  
Skeletal Muscle ◽  
Ionic Strength ◽  
Atpase Activity ◽  
Rabbit Skeletal Muscle ◽  
Ion Concentration ◽  
Actin Binding ◽  
Molar Ratio ◽  
Reversible Inhibitor ◽  
Skeletal Muscle Myosin ◽  
Low Ionic Strength

Tomato activation inhibiting protein (AIP) is a molecule of an apparent molecular weight of 72,000 that co-purifies with tomato actin. In an assay system containing rabbit skeletal muscle F-actin and rabbit skeletal muscle myosin subfragment-1 (myosin S-1), tomato AIP dissociated the acto-S-1 complex in the absence of Mg+2ATP and inhibited the ability of F-actin to activate the low ionic strength Mg+2ATPase activity of myosin S-1. At a molar ratio of 5 actin to 1 AIP, a 50% inhibition of the actin-activated Mg+2ATPase activity of myosin S-1 was observed. The inhibition can be reversed by raising the calcium ion concentration to 1 X 10(-5) M. The AIP had no effect on the basal low ionic strength Mg+2ATPase activity of myosin S-1 in the absence of actin. The protein did not bind directly to actin nor did it cause depolymerization or aggregation of F-actin but appeared, instead, to interact with the actin binding site on myosin S-1. Since AIP is a potent, reversible inhibitor of the rabbit acto-S-1 ATPase activity, it is postulated that it may be responsible for the low levels of actin activation exhibited by tomato F-actin fractions containing the AIP.

scholarly journals Causes of fatigue in slow-twitch rat skeletal muscle during dynamic activity

2009 ◽  
Vol 297 (3) ◽  
pp. R900-R910 ◽  
Author(s):  
Morten Munkvik ◽  
Per Kristian Lunde ◽  
Ole M. Sejersted
Keyword(s):  
Skeletal Muscle ◽  
Isometric Force ◽  
Force Production ◽  
Maximum Force ◽  
Stimulation Protocol ◽  
Shortening Velocity ◽  
Dynamic Activity ◽  
Initial Values ◽  
Isotonic Shortening

Skeletal muscle fatigue is most often studied in vitro at room temperature and is classically defined as a decline in maximum force production or power output, exclusively linked to repeated isometric contractions. However, most muscles shorten during normal use, and we propose that both the functional correlate of fatigue, as well as the fatigue mechanism, will be different during dynamic contractions compared with static contractions. Under isoflurane anesthesia, fatigue was induced in rat soleus muscles in situ by isotonic shortening contractions at 37°C. Muscles were stimulated repeatedly for 1 s at 30 Hz every 2 s for a total of 15 min. The muscles were allowed to shorten isotonically against a load corresponding to one-third of maximal isometric force. Maximal unloaded shortening velocity (V0), maximum force production (Fmax), and isometric relaxation rate (−dF/d t) was reduced after 100 s but returned to almost initial values at the end of the stimulation protocol. Likewise, ATP and creatine phosphate (CrP) were reduced after 100 s, but the level of CrP was partially restored to initial values after 15 min. The rate of isometric force development, the velocity of shortening, and isotonic shortening were also reduced at 100 s, but in striking contrast, did not recover during the remainder of the stimulation protocol. The regulatory myosin light chain (MLC2s) was dephosphorylated after 100 s and did not recover. Although metabolic changes may account for the changes of Fmax, −dF/d t, and V0, dephosphorylation of MLC2s may be involved in the fatigue seen as sustained slower contraction velocities and decreased muscle shortening.

Δ Protein, a New Fibrous Protein of Skeletal Muscle: Preparation

1957 ◽  
Vol 188 (2) ◽  
pp. 205-211 ◽  
Author(s):  
William R. Amberson ◽  
John I. White ◽  
Howard B. Bensusan ◽  
Sylvia Himmelfarb ◽  
Brigitte E. Blankenhorn
Keyword(s):  
Skeletal Muscle ◽  
Ionic Strength ◽  
Electrophoretic Mobility ◽  
Protein A ◽  
High Ionic Strength ◽  
Partial Purification ◽  
Rabbit Muscle ◽  
Muscle Preparation ◽  
Preparative Electrophoresis ◽  
Fibrous Protein

Δ protein, a previously unreported fibrous protein with an electrophoretic mobility greater than that of myosin, is extracted from rabbit muscle by solutions of high ionic strength. This protein forms a complex with myosin, designated as Δ-myosin. Partial purification of Δ protein is achieved by two independent methods. In the first method alcohol fractionation is used. In the second, a solution of Salyrgan is used to dissociate the precipitated Δ-myosin complex. In each method further purification is obtained by preparative electrophoresis. Neither method yields a product which is entirely homogeneous. Tropomyosin is present as a contaminant in alcohol-fractionated preparations, and has been isolated and crystallized. All efforts to derive Δ protein from the previously known fibrous proteins of muscle have failed.

Heat-induced Gelation of Myosins/Subfragments from Chicken Leg and Breast Muscles at High Ionic Strength and Low pH

1991 ◽  
Vol 56 (4) ◽  
pp. 884-890 ◽  
Author(s):  
IL-SHIN CHOE ◽  
JON-ICHIRO MORITA ◽  
KATSUHIRO YAMAMOTO ◽  
KUNIHIKO SAMEJIMA ◽  
TSUTOMU YASUI
Keyword(s):  
Ionic Strength ◽  
Low Ph ◽  
High Ionic Strength

Factors affecting movement of F-actin filaments propelled by skeletal muscle heavy meromyosin

1992 ◽  
Vol 262 (3) ◽  
pp. C714-C723 ◽  
Author(s):  
E. Homsher ◽  
F. Wang ◽  
J. R. Sellers
Keyword(s):  
Skeletal Muscle ◽  
Ionic Strength ◽  
Actin Filament ◽  
Molecular Motors ◽  
Actin Filaments ◽  
Heavy Meromyosin ◽  
Shortening Velocity ◽  
Weakly Bound ◽  
Factors Affecting ◽  
Cross Bridges

The measurement of fluorescent-labeled actin filament movement driven by mechanoenzymes (e.g., myosin) is an important methodology for the study of molecular motors. It is assumed that the filament velocity (Vf) is analogous to the unloaded shortening velocity (Vu) seen in muscle fibers. Methods are described to reproducibly quantitate the movement of these filaments and to select uniformly moving filaments and specify their Vf. Use of these techniques allowed comparison of Vf to literature values for Vu with regard to [ATP], [ADP], [Pi], pH, ionic strength (10-150 mM), and temperature (15-30 degrees C). Vf and Vu are quantitatively similar with respect to the effects of substrate and product concentrations and temperatures greater than 20 degrees C. However, Vf is more sensitive to decreases in pH and temperatures less than 20 degrees C than Vu. At ionic strengths of 50-150 mM, Vf and Vu exhibit similar ionic strength dependencies (decreasing with ionic strength). At ionic strengths less than 50 mM, Vf is markedly reduced. Results of experiments using adenosine 5'-O-(3-thiotriphosphate) suggest that increasing the number of weakly bound cross bridges does not seriously affect Vf. Thus, although Vf is a good analogue for Vu under certain conditions (elevated ionic strength and temperatures greater than 20 degrees C), under others it is not. The results of motility assays must be cautiously interpreted.

Sign in / Sign up

Export Citation Format

Share Document