Cross-Bridges Affect Both TnC Structure and Calcium Affinity in Muscle Fibers

1993 ◽  
pp. 183-194 ◽  
Author(s):  
A. M. Gordon ◽  
E. B. Ridgway
Keyword(s):  
Muscle Fibers ◽  
Calcium Affinity ◽  
Cross Bridges

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.

Effects of BAPTA on force and Ca2+ transient during isometric contraction of frog muscle fibers

1998 ◽  
Vol 275 (2) ◽  
pp. C375-C381 ◽  
Author(s):  
Y.-B. Sun ◽  
C. Caputo ◽  
K. A. P. Edman
Keyword(s):  
Mechanical Performance ◽  
Muscle Fibers ◽  
Frog Muscle ◽  
Clear Correlation ◽  
Bathing Solution ◽  
Control Value ◽  
Contractile System ◽  
Intracellular Ca ◽  
Cross Bridges ◽  
Reduced State

The effects of 1,2-bis(2-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid (BAPTA) on force and intracellular Ca2+ transient were studied during isometric twitches and tetanuses in single frog muscle fibers. BAPTA was added to the bathing solution in its permeant AM form (50 and 100 μM). There was no clear correlation between the changes in force and the changes in Ca2+ transient. Thus during twitch stimulation BAPTA did not suppress the Ca2+ transient until the force had been reduced to <50% of its control value. At the same time, the peak myoplasmic free Ca2+concentration reached during tetanic stimulation was markedly increased, whereas the force was slightly reduced by BAPTA. The effects of BAPTA were not duplicated by using another Ca2+ chelator, EGTA, indicating that BAPTA may act differently as a Ca2+ chelator. Stiffness measurements suggest that the decrease in mechanical performance in the presence of BAPTA is attributable to a reduced number of active cross bridges. The results could mean that BAPTA, under the conditions used, inhibits the binding of Ca2+ to troponin C resulting in a reduced state of activation of the contractile system.

Effect of Pi on unloaded shortening velocity of slow and fast mammalian muscle fibers

2002 ◽  
Vol 282 (4) ◽  
pp. C647-C653 ◽  
Author(s):  
Jeffrey J. Widrick
Keyword(s):  
Fiber Type ◽  
Muscle Fibers ◽  
Medial Gastrocnemius ◽  
Type I ◽  
Shortening Velocity ◽  
Cross Bridge ◽  
Skinned Muscle ◽  
Specific Effects ◽  
Cross Bridges ◽  
Bridge Models

Chemically skinned muscle fibers, prepared from the rat medial gastrocnemius and soleus, were subjected to four sequential slack tests in Ca2+-activating solutions containing 0, 15, 30, and 0 mM added Pi. Pi (15 and 30 mM) had no effect on the unloaded shortening velocity ( V o) of fibers expressing type IIb myosin heavy chain (MHC). For fibers expressing type I MHC, 15 mM Pi did not alter V o, whereas 30 mM Pireduced V o to 81 ± 1% of the original 0 mM Pi value. This effect was readily reversible when Pi was lowered back to 0 mM. These results are not compatible with current cross-bridge models, developed exclusively from data obtained from fast fibers, in which V o is independent of Pi. The response of the type I fibers at 30 mM Pi is most likely the result of increased internal drag opposing fiber shortening resulting from fiber type-specific effects of Pi on cross bridges, the thin filament, or the rate-limiting step of the cross-bridge cycle.

scholarly journals Quantitative electrophoretic analysis of myosin heavy chains in single muscle fibers

2001 ◽  
Vol 90 (5) ◽  
pp. 1927-1935 ◽  
Author(s):  
Boris A. Tikunov ◽  
H. Lee Sweeney ◽  
Lawrence C. Rome
Keyword(s):  
Muscle Fibers ◽  
Electrophoretic Analysis ◽  
Single Fiber ◽  
Fiber Types ◽  
Single Muscle ◽  
Myosin Heavy Chains ◽  
Single Fibers ◽  
Heavy Chains ◽  
Cross Bridges ◽  
Whole Muscle

To better understand the molecular basis of the large variation in mechanical properties of different fiber types, there has been an intense effort to relate the mechanical and energetic properties measured in skinned single fibers to those of their constituent cross bridges. There is a significant technical obstacle, however, in estimating the number of cross bridges in a single fiber. In this study, we have developed a procedure for extraction and quantification of myosin heavy chains (MHCs) that permits the routine and direct measurement of the myosin content in single muscle fibers. To validate this method, we also compared MHC concentration measured in single fibers with the MHC concentration in whole fast-twitch (psoas and gracilis) and slow-twitch (soleus) muscles of rabbit. We found that the MHC concentration in intact psoas (184 μM) was larger than that in soleus (144 μM), as would be expected from their differing mitochondrial content and volume of myofibrils. We obtained excellent agreement between MHC concentration measured at the single fiber level with that measured at the whole muscle level. This not only verifies the efficacy of our procedure but also shows that the difference in concentration at the whole muscle level simply reflects the concentration differences in the constituent fiber types. This new procedure should be of considerable help in future attempts to determine kinetic differences in cross bridges from different fiber types.

scholarly journals Backward Movements of Cross-Bridges by Application of Stretch and by Binding of MgADP to Skeletal Muscle Fibers in the Rigor State as Studied by X-Ray Diffraction

1999 ◽  
Vol 76 (4) ◽  
pp. 1770-1783 ◽  
Author(s):  
Yasunori Takezawa ◽  
Duck-Sool Kim ◽  
Masaki Ogino ◽  
Yasunobu Sugimoto ◽  
Takakazu Kobayashi ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibers ◽  
X Ray Diffraction ◽  
X Ray ◽  
Rigor State ◽  
Skeletal Muscle Fibers ◽  
Cross Bridges

Effects of blebbistatin and Ca2+ concentration on force produced during stretch of skeletal muscle fibers

2010 ◽  
Vol 299 (5) ◽  
pp. C1127-C1135 ◽  
Author(s):  
Fabio C. Minozzo ◽  
Dilson E. Rassier
Keyword(s):  
Skeletal Muscle ◽  
Sarcomere Length ◽  
Muscle Fibers ◽  
Critical Force ◽  
Power Stroke ◽  
Optimal Length ◽  
Maximal Force ◽  
The Cross ◽  
Cross Bridges ◽  
Two Phases

When activated muscle fibers are stretched at low speeds [≤2 optimal length ( Lo)/s], force increases in two phases, marked by a change in slope [critical force (Pc)] that happens at a critical sarcomere length extension ( Lc). Some studies attribute Pc to the number of attached cross bridges before stretch, while others attribute it to cross bridges in a pre-power-stroke state. In this study, we reinvestigated the mechanisms of forces produced during stretch by altering either the number of cross bridges attached to actin or the cross-bridge state before stretch. Two sets of experiments were performed: 1) activated fibers were stretched by 3% Lo at speeds of 1.0, 2.0, and 3.0 Lo/s in different pCa2+ (4.5, 5.0, 5.5, 6.0), or 2) activated fibers were stretched by 3% Lo at 2 Lo/s in pCa2+ 4.5 containing either 5 μM blebbistatin(+/−) or its inactive isomer (+/+). All stretches started at a sarcomere length (SL) of 2.5 μm. When fibers were activated at a pCa2+ of 4.5, Pc was 2.47 ± 0.11 maximal force developed before stretch (Po) and decreased with lower concentrations of Ca2+. Lc was not Ca2+ dependent; the pooled experiments provided a Lc of 14.34 ± 0.34 nm/half-sarcomere (HS). Pc and Lc did not change with velocities of stretch. Fibers activated in blebbistatin(+/−) showed a higher Pc (2.94 ± 0.17 Po) and Lc (16.30 ± 0.38 nm/HS) than control fibers (Pc 2.31 ± 0.08 Po; Lc 14.05 ± 0.63 nm/HS). The results suggest that forces produced during stretch are caused by both the number of cross bridges attached to actin and the cross bridges in a pre-power-stroke state. Such cross bridges are stretched by large amplitudes before detaching from actin and contribute significantly to the force developed during stretch.

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