scholarly journals Troponin and Titin Coordinately Regulate Length-dependent Activation in Skinned Porcine Ventricular Muscle

2008 ◽  
Vol 131 (3) ◽  
pp. 275-283 ◽  
Author(s):  
Takako Terui ◽  
Munguntsetseg Sodnomtseren ◽  
Douchi Matsuba ◽  
Jun Udaka ◽  
Shin'ichi Ishiwata ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Left Ventricular ◽  
Ventricular Muscle ◽  
Passive Force ◽  
Active Force ◽  
Fast Skeletal Muscle ◽  
Thin Filaments ◽  
Cross Bridges ◽  
Length Dependent Activation

We investigated the molecular mechanism by which troponin (Tn) regulates the Frank-Starling mechanism of the heart. Quasi-complete reconstitution of thin filaments with rabbit fast skeletal Tn (sTn) attenuated length-dependent activation in skinned porcine left ventricular muscle, to a magnitude similar to that observed in rabbit fast skeletal muscle. The rate of force redevelopment increased upon sTn reconstitution at submaximal levels, coupled with an increase in Ca2+ sensitivity of force, suggesting the acceleration of cross-bridge formation and, accordingly, a reduction in the fraction of resting cross-bridges that can potentially produce additional active force. An increase in titin-based passive force, induced by manipulating the prehistory of stretch, enhanced length-dependent activation, in both control and sTn-reconstituted muscles. Furthermore, reconstitution of rabbit fast skeletal muscle with porcine left ventricular Tn enhanced length-dependent activation, accompanied by a decrease in Ca2+ sensitivity of force. These findings demonstrate that Tn plays an important role in the Frank-Starling mechanism of the heart via on–off switching of the thin filament state, in concert with titin-based regulation.

scholarly journals Regulatory mechanism of length-dependent activation in skinned porcine ventricular muscle: role of thin filament cooperative activation in the Frank-Starling relation

2010 ◽  
Vol 136 (4) ◽  
pp. 469-482 ◽  
Author(s):  
Takako Terui ◽  
Yuta Shimamoto ◽  
Mitsunori Yamane ◽  
Fuyu Kobirumaki ◽  
Iwao Ohtsuki ◽  
...  
Keyword(s):  
Thin Filament ◽  
Linear Regression Analysis ◽  
Left Ventricular ◽  
Active Force ◽  
Force Measurements ◽  
Systematic Understanding ◽  
Cardiac Sarcomeres ◽  
Length Dependent Activation ◽  
Cooperative Activation

Cardiac sarcomeres produce greater active force in response to stretch, forming the basis of the Frank-Starling mechanism of the heart. The purpose of this study was to provide the systematic understanding of length-dependent activation by investigating experimentally and mathematically how the thin filament “on–off” switching mechanism is involved in its regulation. Porcine left ventricular muscles were skinned, and force measurements were performed at short (1.9 µm) and long (2.3 µm) sarcomere lengths. We found that 3 mM MgADP increased Ca2+ sensitivity of force and the rate of rise of active force, consistent with the increase in thin filament cooperative activation. MgADP attenuated length-dependent activation with and without thin filament reconstitution with the fast skeletal troponin complex (sTn). Conversely, 20 mM of inorganic phosphate (Pi) decreased Ca2+ sensitivity of force and the rate of rise of active force, consistent with the decrease in thin filament cooperative activation. Pi enhanced length-dependent activation with and without sTn reconstitution. Linear regression analysis revealed that the magnitude of length-dependent activation was inversely correlated with the rate of rise of active force. These results were quantitatively simulated by a model that incorporates the Ca2+-dependent on–off switching of the thin filament state and interfilament lattice spacing modulation. Our model analysis revealed that the cooperativity of the thin filament on–off switching, but not the Ca2+-binding ability, determines the magnitude of the Frank-Starling effect. These findings demonstrate that the Frank-Starling relation is strongly influenced by thin filament cooperative activation.

scholarly journals Effects of ramp shortening during linear phase of relaxation on [Ca2+]i in intact skeletal muscle fibers

1999 ◽  
Vol 276 (1) ◽  
pp. C152-C160 ◽  
Author(s):  
Yandong Jiang ◽  
Fred J. Julian
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Sarcomere Length ◽  
Muscle Fibers ◽  
Linear Phase ◽  
Fixed Size ◽  
Skeletal Muscle Fibers ◽  
Straight Line ◽  
Sigmoidal Curve ◽  
Cross Bridges

The effects of shortening distance at V u, the unloaded shortening speed, and filament overlap on the amount of extra Ca2+ released during relaxation in muscle, as indicated by the bump area, were studied. Single, intact frog skeletal muscle fibers at 3°C were used. The myoplasmic free Ca2+ concentration ([Ca2+]i) was estimated by using fura 2 salt injected into the myoplasm. Ramps were applied, either at full overlap with different sizes or at varying overlaps with a fixed size, in the linear phase of relaxation. At full overlap, a plot of bump area vs. ramp size was fit by using a sigmoidal curve with one-half of the bump area equal to 25.9 nm. With a fixed ramp size of 100 nm/half-sarcomere, the plot of bump area vs. mean sarcomere length (SLm) was fit by a straight line intersecting the SLm axis at ∼3.5 μm, close to just no overlap. The results suggest that the transition in the distribution of attached cross bridges from the isometric case to one appropriate for unloaded shortening at V u is completed within 50 nm/half-sarcomere and support the view that attached cross bridges in the overlap zone influence the affinity of Ca2+for troponin C in the thin filament.

Stimulation rate, potentiators, and sarcomere length-tension relationship of muscle

1985 ◽  
Vol 249 (5) ◽  
pp. C497-C502 ◽  
Author(s):  
L. C. Rome ◽  
D. L. Morgan ◽  
F. J. Julian
Keyword(s):  
Thin Filament ◽  
Sarcomere Length ◽  
Rana Temporaria ◽  
Maximal Level ◽  
Stimulation Rate ◽  
Mechanical Interference ◽  
Tension Generation ◽  
Cross Bridges ◽  
Relationship Of ◽  
Length Dependent Activation

Isometric tetani of single muscle fibers of Rana temporaria were studied as a function of stimulation rate, sarcomere length (1.7-2.3 micron), twitch-to-tetanus ratio, and exposure to twitch potentiators (Zn2+ and NO3-) at 20 degrees C. As the stimulation rate was decreased below a maximal level, tension generation decreased. This depression in tension generation was more pronounced at shorter sarcomere lengths. Therefore the magnitude and shape of the sarcomere length curve was dependent on stimulation rate. Although the depression in tension generation was always accompanied by a noticeable ripple in the tension record in fibers with large twitch-to-tetanus ratios, it could be observed even during well-fused tetani in fibers with low twitch-to-tetanus ratios. In all fibers, however, high stimulation rates or exposure to potentiators resulted in maximum tension generation at each length, and the sarcomere length-tension curve followed that found by Gordon, Huxley, and Julian. This indicates that the fall in tension between sarcomere lengths of 2.0 and 1.7 micron is not due to length-dependent activation but is more likely to be the result of mechanical interference in the force-generating interaction between cross bridges and thin filament sites.

The Z band in skeletal muscle in rigor exhibits the activated lattice form

1989 ◽  
Vol 47 ◽  
pp. 252-253
Author(s):  
R. J. Edwards
Keyword(s):  
Skeletal Muscle ◽  
Cross Sections ◽  
Active Tension ◽  
Thin Filaments ◽  
Cross Bridge ◽  
The Cross ◽  
Cross Bridges ◽  
Glycerinated Muscle

The Z band of skeletal muscle is a tetragonal array of interdigitating thin filaments from adjacent sarcomeres held together by cross connecting filaments. Two visually unique forms of the Z band (small square, ss, and basketweave, bw) can be observed by TEM of cross sections. The ss form is found in relaxed muscle and the bw is found in maximally activated muscle. The average Z spacing in the bw form is 20% largerthan in the ss form. There is a correlation between active tension and the form of the Z band. This correlation suggests that cross bridge binding in the A band is directly related to the form of the Z band. In rigor, the cross bridges are completely bound; therefore, we predicted that the Z band would exhibit the bw form. To test this hypothesis we compared unstimulated muscle to glycerinated muscle in rigor.

scholarly journals Reduced thin filament length in nebulin-knockout skeletal muscle alters isometric contractile properties

2009 ◽  
Vol 296 (5) ◽  
pp. C1123-C1132 ◽  
Author(s):  
David S. Gokhin ◽  
Marie-Louise Bang ◽  
Jianlin Zhang ◽  
Ju Chen ◽  
Richard L. Lieber
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Expression Patterns ◽  
Nemaline Myopathy ◽  
Myosin Heavy Chain Isoforms ◽  
Filament Length ◽  
Force Transmission ◽  
Thin Filaments ◽  
Tension Properties ◽  
Tension Curves

Nebulin (NEB) is a large, rod-like protein believed to dictate actin thin filament length in skeletal muscle. NEB gene defects are associated with congenital nemaline myopathy. The functional role of NEB was investigated in gastrocnemius muscles from neonatal wild-type (WT) and NEB knockout (NEB-KO) mice, whose thin filaments have uniformly shorter lengths compared with WT mice. Isometric stress production in NEB-KO skeletal muscle was reduced by 27% compared with WT skeletal muscle on postnatal day 1 and by 92% on postnatal day 7, consistent with functionally severe myopathy. NEB-KO muscle was also more susceptible to a decline in stress production during a bout of 10 cyclic isometric tetani. Length-tension properties in NEB-KO muscle were altered in a manner consistent with reduced thin filament length, with length-tension curves from NEB-KO muscle demonstrating a 7.4% narrower functional range and an optimal length reduced by 0.13 muscle lengths. Expression patterns of myosin heavy chain isoforms and total myosin content did not account for the functional differences between WT and NEB-KO muscle. These data indicate that NEB is essential for active stress production, maintenance of functional integrity during cyclic activation, and length-tension properties consistent with a role in specifying normal thin filament length. Continued analysis of NEB's functional properties will strengthen the understanding of force transmission and thin filament length regulation in skeletal muscle and may provide insights into the molecular processes that give rise to nemaline myopathy.

scholarly journals Calcium ion-regulated thin filaments from vascular smooth muscle

1980 ◽  
Vol 185 (2) ◽  
pp. 355-365 ◽  
Author(s):  
S B Marston ◽  
R M Trevett ◽  
M Walters
Keyword(s):  
Skeletal Muscle ◽  
Smooth Muscle ◽  
Atpase Activity ◽  
Thin Filament ◽  
Troponin I ◽  
Troponin C ◽  
Myosin Atpase ◽  
Protein G ◽  
Thin Filaments ◽  
Myosin Atpase Activity

Myosin and actin competition tests indicated the presence of both thin-filament and myosin-linked Ca2+-regulatory systems in pig aorta and turkey gizzard smooth-muscle actomyosin. A thin-filament preparation was obtained from pig aortas. The thin filaments had no significant ATPase activity [1.1 +/- 2.6 nmol/mg per min (mean +/- S.D.)], but they activated skeletal-muscle myosin ATPase up to 25-fold [500 nmol/mg of myosin per min (mean +/- S.D.)] in the presence of 10(-4) M free Ca2+. At 10(-8) M-Ca2+ the thin filaments activated myosin ATPase activity only one-third as much. Thin-filament activation of myosin ATPase activity increased markedly in the range 10(-6)-10(-5) M-Ca2+ and was half maximal at 2.7 × 10(-6) M (pCa2+ 5.6). The skeletal myosin-aorta-thin-filament mixture gave a biphasic ATPase-rate-versus-ATP-concentration curve at 10(-8) M-Ca2+ similar to the curve obtained with skeletal-muscle thin filaments. Thin filaments bound up to 9.5 mumol of Ca2+/g in the presence of MgATP2-. In the range 0.06-27 microM-Ca2+ binding was hyperbolic with an estimated binding constant of (0.56 +/- 0.07) x 10(6) M-1 (mean +/- S.D.) and maximum binding of 8.0 +/- 0.8 mumol/g (mean +/- S.D.). Significantly less Ca2+ bound in the absence of ATP. The thin filaments contained actin, tropomyosin and several other unidentified proteins. 6 M-Urea/polyacrylamide-gel electrophoresis at pH 8.3 showed proteins that behaved like troponin I and troponin C. This was confirmed by forming interspecific complexes between radioactive skeletal-muscle troponin I and troponin C and the aorta thin-filament proteins. The thin filaments contained at least 1.4 mumol of a troponin C-like protein/g and at least 1.1 mumol of a troponin I-like protein/g.

scholarly journals Tropomodulin is associated with the free (pointed) ends of the thin filaments in rat skeletal muscle.

1993 ◽  
Vol 120 (2) ◽  
pp. 411-420 ◽  
Author(s):  
V M Fowler ◽  
M A Sussmann ◽  
P G Miller ◽  
B E Flucher ◽  
M P Daniels
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Spatial Organization ◽  
Membrane Skeleton ◽  
Filament Length ◽  
Human Erythrocyte Membrane ◽  
Thin Filaments ◽  
Muscle Tropomyosin ◽  
Immunofluorescence Labeling ◽  
Pointed End

The length and spatial organization of thin filaments in skeletal muscle sarcomeres are precisely maintained and are essential for efficient muscle contraction. While the major structural components of skeletal muscle sarcomeres have been well characterized, the mechanisms that regulate thin filament length and spatial organization are not well understood. Tropomodulin is a new, 40.6-kD tropomyosin-binding protein from the human erythrocyte membrane skeleton that binds to one end of erythrocyte tropomyosin and blocks head-to-tail association of tropomyosin molecules along actin filaments. Here we show that rat psoas skeletal muscle contains tropomodulin based on immunoreactivity, identical apparent mobility on SDS gels, and ability to bind muscle tropomyosin. Results from immunofluorescence labeling of isolated myofibrils at resting and stretched lengths using anti-erythrocyte tropomodulin antibodies indicate that tropomodulin is localized at or near the free (pointed) ends of the thin filaments; this localization is not dependent on the presence of myosin thick filaments. Immunoblotting of supernatants and pellets obtained after extraction of myosin from myofibrils also indicates that tropomodulin remains associated with the thin filaments. 1.2-1.6 copies of muscle tropomodulin are present per thin filament in myofibrils, supporting the possibility that one or two tropomodulin molecules may be associated with the two terminal tropomyosin molecules at the pointed end of each thin filament. Although a number of proteins are associated with the barbed ends of the thin filaments at the Z disc, tropomodulin is the first protein to be specifically located at or near the pointed ends of the thin filaments. We propose that tropomodulin may cap the tropomyosin polymers at the pointed end of the thin filament and play a role in regulating thin filament length.

scholarly journals Role of Thin Filament Cooperative Activation in Length-dependent Activation in Skinned Porcine Ventricular Muscle

2009 ◽  
Vol 96 (3) ◽  
pp. 223a
Author(s):  
Takako Terui ◽  
Yuta Shimamoto ◽  
Munguntsetseg Sodnomtseren ◽  
Mitsuhiro Yamane ◽  
Iwao Ohtsuki ◽  
...  
Keyword(s):  
Thin Filament ◽  
Ventricular Muscle ◽  
Length Dependent Activation ◽  
Cooperative Activation
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