scholarly journals Myosin binding-induced cooperative activation of the thin filament in cardiac myocytes and skeletal muscle fibers

1995 ◽  
Vol 68 (4) ◽  
pp. 1430-1442 ◽  
Author(s):  
J.M. Metzger
Keyword(s):  
Skeletal Muscle ◽  
Cardiac Myocytes ◽  
Thin Filament ◽  
Muscle Fibers ◽  
Skeletal Muscle Fibers ◽  
Myosin Binding ◽  
Cooperative Activation

pH dependence of myosin binding-induced activation of the thin filament in cardiac myocytes and skeletal fibers

1996 ◽  
Vol 270 (3) ◽  
pp. H1008-H1014 ◽  
Author(s):  
J. M. Metzger
Keyword(s):  
Skeletal Muscle ◽  
Cardiac Myocytes ◽  
Thin Filament ◽  
Ph Dependence ◽  
Muscle Fibers ◽  
Isometric Tension ◽  
Experimental Conditions ◽  
Skeletal Muscle Fibers ◽  
Myosin Binding ◽  
Fast Twitch

The pH dependence of myosin binding-induced thin filament activation was determined in permeabilized cardiac myocytes and slow- and fast-twitch single skeletal muscle fibers by experimental lowering of [MgATP] in the Ca(2+)-free solutions bathing the permeabilized preparations. As the pS (where S is [MgATP] and pS is -log[MgATP]) was increased from 3.0 to 8.0, isometric tension increased to a peak value in the pS range of 4.9-5.3. At pH 7.00, the transition from the relaxed to the activated rigor state was steep in cardiac myocytes [Hill value (nH) = 21.2 +/- 3.1 (SE)] and due to the apparent effect of strongly bound cross bridges to cooperatively activate the thin filament in the absence of added Ca2+. At pH 6.20, the steepness of the tension-pS relationship was markedly reduced (nH = 6.1 +/- 1.0) and the midpoint of the relationship (pS50) was shifted to higher pS values in cardiac myocytes. In comparison, reduced pH had no effect on the steepness or position of the tension-pS relationship in single slow- or fast-twitch skeletal muscle fibers. These findings suggest that myosin binding-induced activation of the thin filament is pH dependent in cardiac myocytes but not in skeletal muscle fibers under these experimental conditions in which Ca2+ is absent.

scholarly journals Exercise: Teaching myocytes new tricks

2017 ◽  
Vol 123 (2) ◽  
pp. 460-472 ◽  
Author(s):  
Scott K. Powers
Keyword(s):  
Skeletal Muscle ◽  
Exercise Training ◽  
Cardiac Myocytes ◽  
Endurance Exercise ◽  
Ischemia Reperfusion ◽  
Muscle Fibers ◽  
Cardiac Phenotype ◽  
Endurance Exercise Training ◽  
Skeletal Muscle Fibers ◽  
Exercise Induced

Endurance exercise training promotes numerous cellular adaptations in both cardiac myocytes and skeletal muscle fibers. For example, exercise training fosters changes in mitochondrial function due to increased mitochondrial protein expression and accelerated mitochondrial turnover. Additionally, endurance exercise training alters the abundance of numerous cytosolic and mitochondrial proteins in both cardiac and skeletal muscle myocytes, resulting in a protective phenotype in the active fibers; this exercise-induced protection of cardiac and skeletal muscle fibers is often referred to as “exercise preconditioning.” As few as 3–5 consecutive days of endurance exercise training result in a preconditioned cardiac phenotype that is sheltered against ischemia-reperfusion-induced injury. Similarly, endurance exercise training results in preconditioned skeletal muscle fibers that are resistant to a variety of stresses (e.g., heat stress, exercise-induced oxidative stress, and inactivity-induced atrophy). Many studies have probed the mechanisms responsible for exercise-induced preconditioning of cardiac and skeletal muscle fibers; these studies are important, because they provide an improved understanding of the biochemical mechanisms responsible for exercise-induced preconditioning, which has the potential to lead to innovative pharmacological therapies aimed at minimizing stress-induced injury to cardiac and skeletal muscle. This review summarizes the development of exercise-induced protection of cardiac myocytes and skeletal muscle fibers and highlights the putative mechanisms responsible for exercise-induced protection in the heart and skeletal muscles.

scholarly journals Alterations in Ca2+ sensitive tension due to partial extraction of C-protein from rat skinned cardiac myocytes and rabbit skeletal muscle fibers.

1991 ◽  
Vol 97 (6) ◽  
pp. 1141-1163 ◽  
Author(s):  
P A Hofmann ◽  
H C Hartzell ◽  
R L Moss
Keyword(s):  
Skeletal Muscle ◽  
Cardiac Myocytes ◽  
Protein Extraction ◽  
Muscle Fibers ◽  
Extraction Procedure ◽  
Psoas Muscle ◽  
Similar Amount ◽  
C Protein ◽  
Skeletal Muscle Fibers ◽  
Partial Extraction

C-protein, a substantial component of muscle thick filaments, has been postulated to have various functions, based mainly on results from biochemical studies. In the present study, effects on Ca(2+)-activated tension due to partial removal of C-protein were investigated in skinned single myocytes from rat ventricle and rabbit psoas muscle. Isometric tension was measured at pCa values of 7.0 to 4.5: (a) in untreated myocytes, (b) in the same myocytes after partial extraction of C-protein, and (c) in some myocytes, after readdition of C-protein. The solution for extracting C-protein contained 10 mM EDTA, 31 mM Na2HPO2, 124 mM NaH2PO4, pH 5.9 (Offer et al., 1973; Hartzell and Glass, 1984). In addition, the extracting solution contained 0.2 mg/ml troponin and, for skeletal muscle, 0.2 mg/ml myosin light chain-2 in order to minimize loss of these proteins during the extraction procedure. Between 60 and 70% of endogenous C-protein was extracted from cardiac myocytes by a 1-h soak in extracting solution at 20-23 degrees C; a similar amount was extracted from psoas fibers during a 3-h soak at 25 degrees C. For both cardiac myocytes and skeletal muscle fibers, partial extraction of C-protein resulted in increased active tension at submaximal concentrations of Ca2+, but had little effect upon maximum tension. C-protein extraction also reduced the slope of the tension-pCa relationships, suggesting that the cooperativity of Ca2+ activation of tension was decreased. Readdition of C-protein to previously extracted myocytes resulted in recovery of both tension and slope to near their control values. The effects on tension did not appear to be due to disruption of cooperative activation of the thin filament, since C-protein extraction from cardiac myocytes that were 40-60% troponin-C (TnC) deficient produced effects similar to those observed in cells that were TnC replete. Measurements of the tension-pCa relationship in skeletal muscle fibers were also made at a sarcomere length of 3.5 microns which, because of the distribution of C-protein on the thick filament, should eliminate any interaction between C-protein and actin. The effects of C-protein extraction were similar at long and short sarcomere lengths. These data are consistent with a model in which C-protein modulates the range of movement of myosin, such that the probability of myosin binding to actin is increased after its extraction.

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.

scholarly journals Identification of sarcolemma-associated antigens with differential distributions on fast and slow skeletal muscle fibers

1987 ◽  
Vol 104 (4) ◽  
pp. 967-979 ◽  
Author(s):  
DA Schafer ◽  
FE Stockdale
Keyword(s):  
Skeletal Muscle ◽  
Smooth Muscle ◽  
Cardiac Myocytes ◽  
Fiber Type ◽  
Muscle Fibers ◽  
Fiber Types ◽  
In Ovo ◽  
Adult Chicken ◽  
Skeletal Muscle Fibers ◽  
Vascular Structures

We have identified three sarcolemma-associated antigens, including two antigens that are differentially distributed on skeletal muscle fibers of the fast, fast/slow, and slow types. Monoclonal antibodies were prepared using partially purified membranes of adult chicken skeletal muscles as immunogens and were used to characterize three antigens associated with the sarcolemma of muscle fibers. Immunofluorescence staining of cryosections of adult and embryonic chicken muscles showed that two of the three antigens differed in expression by fibers depending on developmental age and whether the fibers were of the fast, fast/slow, or slow type. Fiber type was assigned by determining the content of fast and slow myosin heavy chain. MSA-55 was expressed equally by fibers of all types. In contrast, MSA-slow and MSA-140 differed in their expression by muscle fibers depending on fiber type. MSA-slow was detected exclusively at the periphery of fast/slow and slow fibers, but was not detected on fast fibers. MSA-140 was detected on all fibers but fast/slow and slow fibers stained more intensely suggesting that these fiber types contain more MSA-140 than fast fibers. These sarcolemma-associated antigens were developmentally regulated in ovo and in vitro. MSA-55 and MSA-140 were detected on all primary muscle fibers by day 8 in ovo of embryonic development, whereas MSA-slow was first detected on muscle fibers just before hatching. Those antigens expressed by fast fibers (MSA-55 and MSA-140) were expressed only after myoblasts differentiated into myotubes, but were not expressed by fibroblasts in cell culture. Each antigen was also detected in one or more nonskeletal muscle cell types: MSA-55 and MSA-slow in cardiac myocytes and smooth muscle of gizzard (but not vascular structures) and MSA-140 in cardiac myocytes and smooth muscle of vascular structures. MSA-55 was identified as an Mr 55,000, nonglycosylated, detergent-soluble protein, and MSA-140 was an Mr 140,000, cell surface protein. The Mr of MSA-slow could not be determined by immunoblotting or immunoprecipitation techniques. These findings indicate that muscle fibers of different physiological function differ in the components associated with the sarcolemma. While the function of these sarcolemma-associated antigens is unknown, their regulated appearance during development in ovo and as myoblasts differentiate in culture suggests that they may be important in the formation, maturation, and function of fast, fast/slow, and slow muscle fibers.

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