Alteration of sarcoplasmic reticulum after denervation of chicken pectoralis muscle

FIM: A fatigued-injured muscle model based on the sliding filament theory

Skeletal muscle modeling has a vital role in movement studies and the development of therapeutic approaches. In the current study, a Huxley-based model for skeletal muscle is proposed, which demonstrates the impact of impairments in muscle characteristics. This model focuses on three identified ions: H+, inorganic phosphate Pi, and Ca2+. Modifications are made to actin-myosin attachment and detachment rates to study the effects of H+ and Pi. Additionally, an activation coefficient is included to represent the role of calcium ions interacting with troponin, highlighting the importance of Ca2+. It is found that maximum isometric muscle force decreases by 9.5% due to a reduction in pH from 7.4 to 6.5 and by 47.5% in case of the combination of a reduction in pH and an increase of Pi concentration up to 30 mM, respectively. Then the force decline caused by a fall in the active calcium ions is studied. When only 15% of the total calcium in the myofibrillar space is able to interact with troponin, up to 80% force drop is anticipated by the model. The proposed fatigued-injured muscle model is useful to study the effect of various shortening velocities and initial muscle-tendon lengths on muscle force; in addition, the benefits of the model go beyond predicting the force in different conditions as it can also predict muscle stiffness and power. The power and stiffness decrease by 40% and 6.5%, respectively, due to the pH reduction, and the simultaneous accumulation of H+ and Pi leads to a 50% and 18% drop in power and stiffness.

The denervated muscle: facts and hypotheses. A historical review

Denervation changes in skeletal muscle (atrophy; alterations of myofibrillar expression, muscle membrane electrical properties, ACh sensitivity and excitation-contraction coupling process; fibrillation), and their possible causes are reviewed. All changes can be counteracted by muscle electrostimulation, while denervation-like effects can be caused by the complete conduction block in muscle nerve. These results do not support the hypothesis that the lack of neurotrophic, non-motor factors plays a role in denervation phenomena. Instead they support the view that the lack of neuromotor discharge is the only cause of the phenomena and that neuromotor activity is an essential factor in regulating muscle properties. However, some experimental results cannot apparently be explained by the lack of neuromotor impulses, and may still suggest that neurotrophic influences exist. A hypothesis is that neurotrophic factors, too feeble to maintain a role in completely differentiated, adult muscles, can concur with neuromotor activity in the differentiation of immature, developing muscles.

Effect of 10-day cast immobilization on sarcoplasmic reticulum calcium regulation in humans

This study investigated the effects of 10-day lower limb cast immobilization on sarcoplasmic reticulum (SR) Ca2+ regulation. Muscle biopsies were analysed in eight healthy females for maximal rates of SR Ca2+ release, Ca2+ uptake and Ca2+ ATPase activity at control, during immobilization at day 3 (IM 3), day 6 (IM 6) and day 10 (IM 10). Quadriceps muscle cross-sectional area (CSA) and 1-repetition maximum (1RM) leg extension strength were measured to determine the extent of muscle size and strength adaptations. Muscle CSA and strength decreased following 10 days of immobilization (11.8 and 41.6%, respectively, P < 0.01). A decrease in SR Ca2+ uptake rate (analysed per g wet wt) was found at IM 3 (13.2%, P=0.05), with a further decrease at IM 10 (19.8% from control, P < 0.01). At IM 10, a decrease in SR Ca2+ uptake rate (per mg protein) also occurred (19.9%, P < 0.01). Sarcoplasmic reticulum Ca2+ ATPase activity and rate of Ca2+ release were not altered with 10 days of immobilization. This study observed a decrease in SR Ca2+ uptake rate, muscular atrophy and strength loss over 10 days of immobilization in humans.

Contractile properties of the human triceps surae muscle during simulated weightlessness

The effect of a 120-day period of bed rest on the mechanical properties of human triceps surae muscle was studied in a group of male volunteers (n = 6, mean age 38 years). The results shows that the contractile properties of skeletal muscle in response to disuse change considerably. Time to isometric peak tension of the triceps surae muscle increased from 120 (SEM 3.0)ms to 136 (SEM 2.9)ms (P < 0.01), half relaxation time from 92 (SEM 2.1)ms to 100 (SEM 1.6)ms (P < 0.05) and total contraction time from 440 (SEM 9.9)ms to 540 (SEM 18.7)ms (P < 0.001). Isometric twitch force (Ft) decreased by a mean of 36.7% (P < 0.05), maximal voluntary contraction (MVC) and maximal force (Fmax) by a mean of 45.5% and 33.7%, respectively (P < 0.05-0.01). The value Fmax:Ft ratio increased by 3.6% (nonsignificant). The difference between Fmax and MVC, expressed as a percentage of Fmax and referred to as force deficiency, has also been calculated. Force deficit increased by a mean of 60% (P < 0.001) after bed rest. Force-velocity properties of the triceps surae muscle calculated according to an absolute scale of voluntary and electrically evoked contraction development decreased considerably. The calculations of the same properties on a relative scale did not differ substantially from the initial physiological state. The results would suggest that muscle disuse is associated with both atrophy and a reduction in contractility in the development of Fmax and decreased central (motor) drive. The change in the triceps surae muscle contractile velocity properties may indicate changes in the kinetically active state in the muscles.

Terminal cisternae of denervated rabbit skeletal muscle: alterations of functional properties of Ca2+ release channels

Terminal cisternae (TC) of skeletal muscle represent the specialized compartment from which Ca2+ is released into the myoplasm after a propagated action potential. In this study we have investigated the morphology, protein composition, and Ca2+ release properties of TC isolated from rabbit gastrocnemius muscle 2 wk after nerve sectioning. Thin-section electron microscopy showed that TC vesicles from denervated muscle were enriched in calsequestrin (CS) and contained a larger fraction of the junctional sarcoplasmic reticulum (SR), as judged by membrane profiles with morphologically intact feet structures. Accordingly, the yield of junctional SR from denervated muscle was twice that of control muscle, and the protein pattern of TC vesicles exhibited an increase in junctional protein components, e.g., CS and the 350-kDa protein. The larger content of the 350-kDa protein, or ryanodine receptor (F.A. Lai, H. Erickson, E. Rousseau, Q.-Y. Liu, and G. Meissner, Nature Lond. 331: 315-319, 1988; T. Imagawa, J. S. Smith, R. Coronado, and K. P. Campbell. J. Biol. Chem. 262: 10636-10643, 1987; L. Hymel, M. Inui, S. Fleischer, and H. Schindler, Proc. Natl. Acad. Sci. USA 85:441-445, 1988) was paralleled by an increased binding site density (Bmax) for ryanodine binding in denervated muscle TC. The effects of ruthenium red, a Ca2+ release blocker, on Ca2+ loading rate and Ca2+-ATPase activity suggested that TC from denervated muscle were less permeable to Ca2+. After active Ca2+ loading, both doxorubicin and caffeine induced Ca2+ release from isolated TC, yet Ca2+ release rates were reduced in denervated muscle TC.(ABSTRACT TRUNCATED AT 250 WORDS)

Sarcoplasmic reticulum of human skeletal muscle: age-related changes and effect of training

The effect of ageing on human skeletal muscle was investigated using needle biopsies from young and aged subjects and from aged subjects trained with different activity patterns. Histochemical staining for myofibrillar ATPase of ageing m. vastus lateralis demonstrated an unchanged fibre type distribution but a selective atrophy of type IIa and type IIb fibres. Analysis of myosin heavy chain (MHC) composition showed that type I MHC increased with ageing (P less than 0.05). The relative content of the MHC isoforms correlated with the relative area of the respective fibre types. Sarcoplasmic reticulum (SR) proteins were investigated in muscle extracts by electrophoretic and immunoblotting techniques. When compared to a young control group (28 +/- 0.1 years old, n = 7) blots of post-myofibrillar supernatant proteins probed with polyclonal antibodies to the rabbit fast SR Ca-ATPase, a marker of extrajunctional SR, showed that the content of Ca-ATPase was significantly lower (P less than 0.05) in the old control group (68 +/- 0.5 years old, n = 8). On the other hand the content of calsequestrin (CS), the major intraluminal protein of SR terminal cisternae (TC), and of the 350-kDa ryanodine-binding protein, which is localized in the junctional regions of TC, did not show a concomitant decrease. These results suggest that ageing differentially affects extrajunctional and junctional SR of human skeletal muscle. These age-related changes were not observed within a group of old strength-trained subjects.

Denervation-induced proliferative changes of triads in rabbit skeletal muscle

Protein compositional and functional differences exist between longitudinal and junctional sarcoplasmic reticulum (SR) in relation to Ca transport and to Ca release. In light of this knowledge, we have reinvestigated the effects of denervation on SR of rabbit gastrocnemius, a predominantly fast muscle. Electron microscopy of 2-weeks denervated muscle showed proliferation of transverse tubules (TT), forming junctional contacts with SR terminal cisternae (TC). At coincident periods, the yield of muscle microsomes was increased, and their fractionation by sucrose-density centrifugation demonstrated a relative increase of heavy vesicles. Thin-section electron microscopy of heavy SR from denervated muscle showed an increased number of vesicles containing calsequestrin (CS) as compared with control muscle. Electrophoretic analysis confirmed the relative decrease of Ca-ATPase protein and the striking increase of CS both in total microsomes and in heavy SR vesicles. Calcium loading and Ca-ATPase activity as well as the density of Ca-ATPase protein were decreased to a similar extent (20-30%) in denervated muscle microsomes. Stimulation of Ca-ATPase activity by Ca-ionophore A23187 showed that the vesicles were tightly sealed. When probed by competitive ELISA with antibody to SR Ca-ATPase from pure fast muscle, the Ca-ATPase of denervated microsomes was found to be highly cross reactive. Cleveland's peptide maps of the Ca-ATPase protein after partial digestion with S. aureus V8 protease also showed no significant change after denervation. Changes in cholesterol content and in the ratio of Mg-ATPase to Ca-ATPase activity of denervated muscle microsomes indicated a 4-fold increase of TT protein, i.e., from about 3% to not more than 12% of total protein, at 2 weeks after denervation. All these changes were totally reversed upon reinnervation of muscle fibers, and the consequent muscle recovery, as obtained by nerve crushing instead of nerve sectioning. From these results, we conclude that denervated adult fast muscle, similarly to immature fast muscle, contains more junctional SR. However, the molecular and catalytic properties of the Ca-ATPase are unaffected by denervation.

Myopathy caused by a deficiency of Ca2+-adenosine triphosphatase in sarcoplasmic reticulum (Brody's disease)

Four male patients from two families were first seen with impaired skeletal muscle relaxation that rapidly worsened during exercise. Muscle biopsies from 2 patients were examined by appropriate biochemical and microscopic immunocytochemical techniques. The adenosine triphosphate (ATP)-dependent Ca2+ transport rate was extremely low in a particulate membrane fraction of skeletal muscle, and there was also a marked reduction of the concentration of 100-kD phosphoprotein, corresponding to Ca2+-ATPase of sarcoplasmic reticulum, in muscle microsomes. The concentration of immunoreactive Ca2+-ATPase of sarcoplasmic reticulum was markedly reduced on immunoblots. Evaluation by microscopic immunocytochemical techniques, using one polyclonal and two monoclonal antibodies against sarcoplasmic reticulum Ca2+ transport protein, revealed that the severe reduction of immunoreactive Ca2+-ATPase was limited to the histochemical type 2 fibers. The deficiency of the Ca2+ transport protein in the sarcoplasmic reticulum of type 2 fibers, which may be the primary expression of a presumed gene defect, can explain the impaired muscle relaxation of the patients. This disease appears to be a clinically, electromyographically, and biochemically distinct metabolic myopathy.

Influences of inactivity and indomethacin on soleus phosphatidylethanolamine and size

Results of previous investigations indicate that muscular prostaglandins (PG) E2 and F2 alpha are biosynthesized during changes in muscular activity and stimulate protein degradation and synthesis, respectively. The results of the present investigation demonstrates a reduction by indomethacin of soleus hypertrophy, which occurred during a one week recovery period following rat hindlimb suspension. While this hypertrophic model evoked significant, rapid increases in soleus myosin and weight in control groups, continuous systemic release of indomethacin (3.5 mg/Kg/day) reduced the gain in soleus weight, Type I and II hypertrophy. Body weights of all groups were not significantly different. Additional analysis found a selective reduction in phosphatidylethanolamine (PE) during soleus atrophy and hypertrophy which were elicited by hindlimb suspension and recovery from suspension, respectively. Indomethacin enhanced PE recovery. Data from previous and present studies support a hypothesis that a change in soleus activity elicits PE catabolism, changes in cytosolic and muscular calcium, in calcium-dependent phospholipase activity, in PG biosynthesis, and in soleus size.

Calcium-related abnormalities in fast and slow denervated skeletal muscle in rats

Muscle weights, Ca-ATPase activity and calcium-binding proteins were studied after denervation in rat extensor digitorum longus (EDL) and soleus (Sol) muscles. Muscle weights decreased progressively as a function of denervation time: after 28 days EDL weight diminished by 70% and Sol weight by 47%. Ca-ATPase activity and calsequestrin were quite reduced in control Sol as compared to the control EDL. Denervation caused a considerable reduction in Ca-ATPase and calsequestrin in EDL, making it resemble the control Sol.

Phosphorylation of the sarcolemma of dystrophic and normal hamster muscle following denervation

The rapid phosphorylation at 0 degree C of sarcolemma preparations of hamster leg muscle was compared with (Na+,K+)-ATPase activity in sham-operated and 7-day denervated muscle. The phosphorylation appeared to be under the trophic influence of the sciatic nerve since the denervated preparations exhibited a markedly reduced phosphorylation. In similar studies using dystrophic hamsters the sarcolemma preparations from sham-operated and denervated leg muscle both exhibited the same degree of phosphorylation.

The ratio between intrinsic 115 kDa and 30 kDa peptides as a marker of fibre type-specific sarcoplasmic reticulum in mammalian muscles

Sarcoplasmic reticulum displays characteristic differences in Ca2+-uptake, Ca2+-ATPase and the pattern of membrane proteins in type I, IIA and IIB fibres. The ratio between the 115 kDa Ca2+-ATPase and a 30 kDa protein is of characteristic magnitude in the sarcoplasmic reticulum of the three fibre types in rat muscles. The slow-to-fast fibre type transformation observed in rabbits during chronic nerve stimulation is accompanied by predictable changes of this ratio.