Contraction transients of skinned muscle fibers: effects of calcium and ionic strength.

Calcium and ionic strength are both known to modify the force developed by skinned frog muscle fibers. To determine how these parameters affect the cross-bridge contraction mechanism, the isotonic velocity transients following step changes in load were studied in solutions in which calcium concentration and ionic strength were varied. Analysis of the motion showed that calcium has no effect on either the null time or the amplitude of the transients. In contrast, the transient amplitude was increased in high ionic strength and was suppressed in low ionic strength. These results are consistent with the idea that calcium affects force in skeletal muscle by modulating the number of force generators in a simple switchlike "on-off" manner and that the steady force at a given calcium level is proportional to cross-bridge number. On the other hand, the effect of ionic strength on force is associated with changes in the kinetic properties of the cross-bridge mechanism.

Download Full-text

Ionic Strength and the Contraction Kinetics of Skinned Muscle Fibers

The Journal of General Physiology ◽

10.1085/jgp.63.4.509 ◽

1974 ◽

Vol 63 (4) ◽

pp. 509-530 ◽

Cited By ~ 55

Author(s):

Marc D. Thames ◽

Louis E. Teichholz ◽

Richard J. Podolsky

Keyword(s):

Ionic Strength ◽

Muscle Fibers ◽

Bathing Solution ◽

Shortening Velocity ◽

Skinned Muscle ◽

Cross Bridges ◽

Low Ionic Strength ◽

Contraction Cycle ◽

Kinetics Of ◽

Contraction Kinetics

The influence of KCl concentration on the contraction kinetics of skinned frog muscle fibers at 5–7°C was studied at various calcium levels. The magnitude of the calcium-activated force decreased continuously as the KCl concentration of the bathing solution was increased from 0 to 280 mM. The shortening velocity at a given relative load was unaffected by the level of calcium activation at 140 mM KCl, as has been previously reported by Podolsky and Teichholz (1970. J. Physiol. [Lond.]. 211: 19), and was independent of ionic strength when the KCl concentration was increased from 140 to 280 mM. In contrast, the shortening velocity decreased as the KCl concentration was reduced below 140 mM; the decrease in velocity was enhanced when the fibers were only partially activated. In the low KCl range, the resting tension of the fibers increased after the first contraction cycle. The results suggest that in fibers activated at low ionic strength some of the cross bridges that are formed are abnormal in the sense that they retard shortening and persist in relaxing solution.

Download Full-text

The Cross-Bridge Mechanism Studied by Flash Photolysis of Caged ATP in Skeletal Muscle Fibers.

The Japanese Journal of Physiology ◽

10.2170/jjphysiol.47.405 ◽

1997 ◽

Vol 47 (5) ◽

pp. 405-415

Author(s):

K. HORIUTI

Keyword(s):

Skeletal Muscle ◽

Flash Photolysis ◽

Muscle Fibers ◽

Caged Atp ◽

Cross Bridge ◽

Skeletal Muscle Fibers ◽

The Cross ◽

Cross Bridge Mechanism

Download Full-text

The Capacitance of Skeletal Muscle Fibers in Solutions of Low Ionic Strength

The Journal of General Physiology ◽

10.1085/jgp.59.3.347 ◽

1972 ◽

Vol 59 (3) ◽

pp. 347-359 ◽

Cited By ~ 8

Author(s):

P. C. Vaughan ◽

J. N. Howell ◽

R. S. Eisenberg

Keyword(s):

Skeletal Muscle ◽

Ionic Strength ◽

Surface Membrane ◽

Muscle Fibers ◽

External Solution ◽

Rectangular Pulse ◽

Bathing Solution ◽

Skeletal Muscle Fibers ◽

Tubular System ◽

Low Ionic Strength

The capacitance of skeletal muscle fibers was measured by recording with one microelectrode the voltage produced by a rectangular pulse of current applied with another microelectrode. The ionic strength of the bathing solution was varied by isosmotic replacement of NaCl with sucrose, the [K] [Cl] product being held constant. The capacitance decreased with decreasing ionic strength, reaching a value of some 2 µF/cm2 in solutions of 30 mM ionic strength, and not decreasing further in solutions of 15 mM ionic strength. The capacitance of glycerol-treated fibers did not change with ionic strength and was also some 2 µF/cm2. It seems likely that lowering the ionic strength reduces the capacitance of the tubular system (defined as the charge stored in the tubular system), and that the 2 µF/cm2 which is insensitive to ionic strength is associated with the surface membrane. The tubular system is open to the external solution in low ionic strength solutions since peroxidase is able to diffuse into the lumen of the tubules. Twitches and action potentials were also recorded from fibers in low ionic strength solutions, even though the capacitance of the tubular system was very small in these solutions. This finding can be explained if there is an action potential—like mechanism in the tubular membrane.

Download Full-text

Regulation of the cross-bridge transition from a weakly to strongly bound state in skinned rabbit muscle fibers

AJP Cell Physiology ◽

10.1152/ajpcell.1995.269.6.c1532 ◽

1995 ◽

Vol 269 (6) ◽

pp. C1532-C1539 ◽

Cited By ~ 78

Author(s):

M. Regnier ◽

C. Morris ◽

E. Homsher

Keyword(s):

Muscle Fibers ◽

Bound State ◽

Single Step ◽

Rabbit Muscle ◽

Weakly Bound ◽

Cross Bridge ◽

Skinned Muscle ◽

Butanedione Monoxime ◽

Bridge Models ◽

Parallel Fashion

The regulation of cross-bridge transition from weakly attached to force-bearing states was studied at 10 degrees C in skinned muscle fibers by measuring the rate of force development after a quick release-restretch cycle (ktr), the rate of force decline (kPi) after photogeneration of Pi from caged Pi, and stiffness in the presence and absence of an inhibitor of strong cross-bridge formation, 2,3-butanedione monoxime (BDM). Both BDM and Pi suppressed force more than stiffness. However, reduction of Ca2+ suppressed force and stiffness in a parallel fashion. Both ktr and kPi were reversibly reduced (by 30-35%) in 3 mM BDM, but both were increased by increasing Pi concentration. Reduction of Ca2+ concentration to match the force seen in 3 mM BDM had no effect on kPi but decreased ktr by 85%. These results are inconsistent with cross-bridge models undergoing the transition from a weakly bound to a force-generating state in a single step but are consistent with a model having two steps, one of which is controlled by pCa.

Download Full-text

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

AJP Cell Physiology ◽

10.1152/ajpcell.00186.2001 ◽

2002 ◽

Vol 282 (4) ◽

pp. C647-C653 ◽

Cited By ~ 19

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.

Download Full-text

Isotonic contraction of skinned muscle fibers on a slow time base: effects of ionic strength and calcium.

The Journal of General Physiology ◽

10.1085/jgp.78.3.233 ◽

1981 ◽

Vol 78 (3) ◽

pp. 233-257 ◽

Cited By ~ 31

Author(s):

J Gulati ◽

R J Podolsky

Keyword(s):

Ionic Strength ◽

Initial Velocity ◽

Muscle Fibers ◽

Time Base ◽

Bathing Solution ◽

Slow Time ◽

Relative Load ◽

Residual Tension ◽

High Calcium ◽

Low Ionic Strength

The force development by calcium-activated skinned frog skeletal muscle fibers and the motion on a slow time base after a quick decrease in load were studied at 0-1 degrees C as a function of the ionic strength and the degree of activation. The ionic strength was varied between 50 and 190 mM by adding appropriate concentrations of KCl to the bathing solution. Under these conditions, the fibers could be maximally activated for several cycles at low ionic strength without developing residual tension. We found that the steady isometric force in fully activated fibers linearly decreased when the KCl concentration was increased from 0 to 140 mM. The steady isotonic motion at a given relative load in fully activated fibers was almost the same at KCl concentration greater than or equal to 50 mM. In 0 and 20 mM KCl, the isotonic velocity decreased continuously for more than 300 ms. At a given relative load, the initial velocity of the motion in 0 and 20 mM KCl was about 0.6 and 0.9 times, respectively, that in 140 mM KCl. The initial velocity decreased further when residual tension developed; this observation provides additional evidence that residual tension may reflect the presence of an internal load. The effect of calcium on the motion was examined at 70 mM KCl. In this solution, the motion during the velocity transient at a given relative load appeared to be the same at different levels of activation. The speed of the subsequent motion was almost steady at high calcium levels but decreased continuously in low calcium levels. These results support the idea that at low ionic strength the response of the fiber to calcium is switch-like, but that other factors also affect the contraction mechanism under these conditions.

Download Full-text

Mathematical aspects of the cross-bridge mechanism in muscle contraction

Nonlinear Analysis ◽

10.1016/0362-546x(83)90048-2 ◽

1983 ◽

Vol 7 (6) ◽

pp. 661-683 ◽

Cited By ~ 16

Author(s):

Valeriano Comincioli ◽

Alessandro Torelli

Keyword(s):

Muscle Contraction ◽

Cross Bridge ◽

The Cross ◽

Cross Bridge Mechanism

Download Full-text

Evidence from Insect Fibrillar Muscle about the Elementary Contractile Process

The Journal of General Physiology ◽

10.1085/jgp.50.6.139 ◽

1967 ◽

Vol 50 (6) ◽

pp. 139-156 ◽

Cited By ~ 9

Author(s):

J. W. S. Pringle

Keyword(s):

Ionic Strength ◽

Atpase Activity ◽

Striated Muscle ◽

Contractile Activity ◽

High Elasticity ◽

Flight Muscles ◽

The Cross ◽

Cross Bridges ◽

Low Ionic Strength ◽

Water Bugs

Bundles of myofibrils prepared from the dorsal longitudinal flight muscles of giant water bugs show oscillatory contractile activity in solutions of low ionic strength containing ATP and 10-8-10-7 M Ca2+. This is due to delay between changes of length and changes of tension under activating conditions. The peculiarities of insect fibrillar muscle which give rise to this behavior are (1) the high elasticity of relaxed myofibrils, (2) a smaller degree of Ca2+ activation of ATPase activity in unstretched myofibrils and extracted actomyosin, and (3) a direct effect of stretch on ATPase activity. It is shown that the cross-bridges of striated muscle are probably formed from the heads of three myosin molecules and that in insect fibrillar muscle the cycles of mechanochemical energy conversion in the cross-bridges can be synchronized by imposed changes of length. This material is more suitable than vertebrate striated muscle for a study of the nature of the elementary contractile process.

Download Full-text