Regulation of glucose uptake in rat slow and fast skeletal muscles

1. Regulation of glucose uptake was compared between extensor digitorum longus (EDL) and soleus (Sol) muscles in rats. 2. Insulin stimulated glucose uptake more in EDL than in Sol. 3. Under high concentrations of insulin, the glucose uptake was higher in EDL than Sol. 4. Inhibition of oxidative phosphorylation by anoxia or an uncoupler stimulated glucose uptake more in EDL than in Sol. 5. Anoxia abolished the effect of insulin on glucose uptake in both EDL and Sol. 6. The blocker to glucose transport system reduced glucose uptake more in Sol than in EDL.     

Properties of intratetanic individual contractile responses in rat slow skeletal muscles during modulation of sarcoplasmic reticulum Ca<Superscript>2+</Superscript> release

In control experiments (n = 16), during direct stimulation of m. Soleus by trains of 5, 10 and 50 stimuli at a rate of 20 Hz a biphasic change was detected in the amplitude of the last contractile responses (LCR_N) depending on N, where N is the number of individual contractile responses in the tetanus. Thus, an initial decrease in LCR_N amplitudes (down to 54 ± 8% for LCR₅) was followed by a subsequent increase (up to 218 ± 14% for LCR₅₀) and significant shortening of their half-relaxation time compared to the initial response (down to 44 ± 8% for LCR₅₀). Caffeine at concentrations of 5 (n = 6) and 10 (n = 4) mM exacerbated LCR₅ depression (down to 31 ± 8% and 15 ± 4%, respectively) against the background of arising characteristic stationary contracture responses. The subsequent increase in the LCR_N amplitude was substantially lower than in control experiments (114 ± 18% and 46 ± 9% for LCR₅₀ compared to the initial response at 5 and 10 mM of caffeine, respectively). The LCR₅₀ half-relaxation time during the effect of caffeine at both concentrations also remained considerably shorter than that of individual responses recorded both in the presence of caffeine and in control experiments. In contrast to the control and caffeine effects, LCR₅ and LCR₁₀ amplitudes during the effect of 10 μM of dantrolene (n = 5) remained at the level close to that of the first response (102 ± 7% and 106 ± 8%, respectively), while the LCR₅₀ amplitude displayed a considerably smaller increase (to 143 ± 14%) than observed in control muscles. Besides, dantrolene further enhanced muscle relaxation at rest. Caffeine (10 mM), as applied in the presence of dantrolene, restored the dynamics of changes in amplitude–temporal characteristics of last contractile responses to values approximating those in control. The amplitude–temporal characteristics of action potentials recorded extracellularly in individual m. Soleus muscle fibers did not change significantly during the transition from single to train stimulation under the same protocol as in mechanographic experiments. These data may be interpreted in support of the previously advanced hypothesis on the implication of Ca²⁺-induced Ca²⁺ release in skeletal muscles under their tetanic stimulation as an additional mechanism of excitation–contraction coupling [1, 2].     

Effect of insulin on characteristics of contractile responses of fast and slow skeletal muscles of rats with acute streptozotocin-induced diabetes

Comparison of amplitude-time characteristics of fast extensor digitorum longus muscles (m. EDL) isolated from control rats and rats with model of acute streptozotocin-induced diabetes mellitus (DM) 12 and 30 days after treatment with streptozotozin did not reveal significant changes of strength of single normalized contractile responses as compared with control. In slow (m. Soleus) muscles of rats with the 30-day long SD, essential changes of the amplitude-time characteristics of such contractile responses were observed: a decrease of their amplitude and an increase of duration. In the diabetic rats treated with insulin there develops resistance of skeletal muscles of both types to action of exogenous insulin. Both in control and in diabetic animals the exhausting stimulation of m. EDL with trains from 5 impulses did not reveal significant differences at early (up to 3 min) terms of development of fatigue. Under similar conditions, fatigue of m. Soleus in rats of the both diabetic groups developed significantly faster as compared with control (already in 30 s after the beginning of stimulation). Insulin at a concentration of 0.5–1 nM produced a dose-dependent decrease of amplitude of single contractile responses in fast and slow muscles of rats with the acute SD model (the negative inotropic action). Earlier, we demonstrated in healthy rats the similar action of insulin, but at the higher concentrations [1]. Insulin at a concentration of 10 nM did not produce an essential effect on dynamics of depression of responses in the course of development of fatigue at tetanical stimulation of m. EDL and m. Soleus both in control and in diabetic rats, but affected essentially the dynamics of change of duration of the half-decay (T_hd) of their tetanical responses. The presence of insulin in the washing solution led to stabilization of the period of muscle relaxation in the course of development of fatigue in all studied animal groups.     

Myosin light chain phosphorylation during contraction of chicken fast and slow skeletal muscles

A modified automatic freezing apparatus (K. M. Kretzschmar and D. R. Wilkie, 1962, J. Physiol. (London), 202, 66–67) was used for studying light chain phosphorylation during the early phase of contraction of the fast, posterior latissimus dorsi, and slow, anterior latissimus dorsi, muscles of chicken at 37 °C. The frozen muscles were worked up under conditions which avoid artifacts in quantitating the level of light chain phosphorylation in contracting and resting muscles. The posterior latissimus dorsi muscle reached 80% of its maximal isometric tension at 0.1 s of tetanic stimulation. At the same time, light chain phosphorylation increased by 60% of its maximal extent. The peak tension of the posterior muscle at 0.2 s of stimulation was accompanied by maximal light chain phosphorylation. In case of the slow anterior latissimus dorsi muscle, maximal tetanic tension was developed in 2.5 – 5 s and light chain phosphorylation also proceeded at a much slower rate than in the fast posterior muscle. When contralateral posterior latissimus dorsi muscles were stimulated for 0.2 s and one muscle was frozen at the height of tetanus while the other muscle was allowed to relax and frozen 0.4 s after terminating the stimulation, both contracted and relaxed muscles exhibited maximal light chain phosphorylation. However, when the muscle was allowed to relax for 0.8 s before freezing, half of the phosphorylated light chain became dephosphorylated. The resting level of phosphate content of the light chain was restored in both the posterior and anterior muscles during a longer time after relaxation.     

Histochemical heterogeneity of intrafusal muscle fibres in slow and fast skeletal muscles of the rat

Summary Intrafusal muscle fibres of the slow soleus (Sol) and fast vastus lateralis (VL) muscles of the rat were studied histochemically. Serial transverse sections were incubated for the localization of succinate dehydrogenase (SDH), alpha glycerophosphate dehydrogenase (GPD) and adenosine triphosphatase (ATPase). The latter was examined further after preincubation in acidic solution held at either low or room temperature (R_T). The bag₂ intrafusal fibres in both muscles displayed high regular and acid stable ATPase, but low SDH and GPD activities. Bag₁ intrafusal fibres showed low to moderate regular ATPase, a regional heterogeneity after R_T acid preincubation (low activity in juxtaequatorial and high in polar zones), moderate SDH, but low GPD reactions. In both muscles the chain fibres usually exhibited high ATPase for both regular and cold acid preincubated reactions, but usually low activity after R_T acid preincubation; they had high SDH but variable GPD activities. In Sol muscle, however, approximately 25% of spindles contained chain fibres that showed high acid-stable ATPase reaction after both cold and R_T acid preincubation. In contrast, chain fibres in some VL spindles had a characteristically low ATPase reaction even after cold acid preincubation. This study, therefore, has delineated the existence of an inherent heterogeneity among chain fibres (with respect to their histochemical reactions) in muscle spindles located within slow and fast muscles and also between those found within populations of either Sol or VL muscle spindles.     

Calpain activity in fast, slow, transforming, and regenerating skeletal muscles of rat

Fiber-type transitions in adult skeletal muscleinduced by chronic low-frequency stimulation (CLFS) encompasscoordinated exchanges of myofibrillar protein isoforms. CLFS-inducedelevations in cytosolic Ca²⁺ could activate proteases,especially calpains, the major Ca²⁺-regulated cytosolicproteases. Calpain activity determined by a fluorogenic substrate inthe presence of unaltered endogenous calpastatin activities increasedtwofold in low-frequency-stimulated extensor digitorum longus (EDL)muscle, reaching a level intermediate between normal fast- andslow-twitch muscles. µ- and m-calpains were delineated by acalpain-specific zymographical assay that assessed total activitiesindependent of calpastatin and distinguished between native andprocessed calpains. Contrary to normal EDL, structure-bound, namelymyofibrillar and microsomal calpains, were abundant in soleus muscle.However, the fast-to-slow conversion of EDL was accompanied by an earlytranslocation of cytosolic µ-calpain, suggesting that myofibrillarand microsomal µ-calpain was responsible for the twofold increase inactivity and thus involved in controlled proteolysis during fibertransformation. This is in contrast to muscle regeneration wherem-calpain translocation predominated. Taken together, we suggest thattranslocation is an important step in the control of calpain activityin skeletal muscle in vivo.

     

Power outputs of slow and fast skeletal muscles of mice

The purpose of this study was to contrast the frequency-power relationship of slow soleus and fast extensor digitorum longus (EDL) muscles to their frequency-force relationships and to investigate factors involved in the development of maximum power during a single contraction. Stimulation frequency-force and stimulation frequency-power relationships were determined for soleus and EDL muscles of the mouse for single contractions in situ at 35 degrees C. Power was measured during isovelocity shortening contractions with displacement through 10% of fiber length at the optimum velocity. Optimum velocity was defined as the shortening velocity for the generation of maximum power for a given stimulation frequency. Both force (N/cm2) and power (watts/kg) increased with stimulation frequency until a plateau was reached. For the frequency-force relationship, the curve for soleus muscles was merely shifted to the left of that for EDL muscles. In contrast, the power developed by EDL muscles was greater than that of soleus muscles (P less than 0.05) at each stimulation frequency. The higher power was a direct consequence of higher optimum velocities for EDL muscles compared with soleus muscles.     

大鼠骨骼肌快肌肌钙蛋白T的同工型

骨骼肌快肌的收缩主要是由钙离子通过肌钙蛋白所调节控制。这些肌钙蛋白位于肌纤维之中。肌蛋白包括肌钙蛋白T、肌钙蛋白C、肌钙蛋白I。采用双向聚丙烯酰胺凝胶电泳和免疫学技术,对大鼠胚胎、新生大鼠和成年大鼠的骨能肌快肌肌钙蛋白T的同工型进行了研究。在成年大鼠的骨能肌快肌中,发现了10种肌钙蛋白T同工型。在大鼠胚胎和新生大鼠的骨能肌中,发现了7种肌钙蛋白T同工型。作为不同动物、不同发育阶段和不同组织发育的特殊标记,这些肌钙蛋白T同工型具有重要意义[动物学报49(3)：362—369,2003]。     

Enzymatic activities in slow and fast denervated old rat muscles

The activities of five enzymes have been studied quantitatively in denervated extensor digitorum longus, gastrocnemius and soleus muscles of 24-month-old rats. The results have been compared with those obtained from normal muscles of a similar age group of rats. Three weeks after denervation, the activity of hexokinase was increased in gastrocnemius and extensor digitorum longus. Phosphofructokinase, lactate dehydrogenase, malate dehydrogenase and 3-hydroxyacyl-CoA-dehydrogenase showed decreased activities. These results suggest that enzyme which represents glucose uptake increased its activity in fast muscles and that enzymes for anaerobic glycolysis, lactate fermentation, citric acid cycle and beta-oxidation had a decreased activity in slow and fast muscles.     

Thyroidal and neural control of myosin transitions during development of rat fast and slow muscles

The uptake of 125I-labeled epidermal growth factor (125I-EGF) by mouse pancreatic acini was inhibited (40-50%) by the secretagogue cholecystokinin octapeptide (CCK8). Analysis of competitive binding data showed that the apparent Kd of EGF binding increased 135% while the binding capacity was only slightly altered (30% increase). That the effect of CCK8 on acini was mediated by intracellular Ca2+ was indicated by the following: (i) Inhibition of 125I-EGF binding to acini was dose-dependent and paralleled the known abilities of CCK8, its analogs, and the cholinergic secretagogue carbachol to induce Ca2+ efflux from acini; and (ii) addition of the Ca2+ ionophore A23187 also inhibited 125I-EGF binding. In addition, EGF association with A431 cells was also inhibited by A23187 in the presence but not the absence of Ca2+.     

The effects of glycerol and urea on the ultrastructure and contractility of fast and slow rat skeletal muscles

The influence of the influx and efflux of glycerol and urea (400 mmol/l) on the amplitude of isometric twitches and the ultrastructure of isolated fast (EDL) and slow (SOL) muscles of young rats was studied. The influx of non-electrolytes was accompanied by a temporary decrease in the twitch tension. The removal of non-electrolytes resulted in a stable reduction of twitches. Both effects were less pronounced in glycerol experiments on slow muscles. The inhibition of twitches after the removal of non-electrolytes was associated with selective alterations of the T-system: swelling, vacuolation, and lysis of T-tubules. Quantitative analysis of the T-system showed that the extent of these changes may vary for different fibres, and the intensity of morphological alteration of the T-system generally correlated with the degree of twitch inhibition. Reloading of muscles with non-electrolytes tended to improve the T-system structure in some fibres and led to a partial restoration of the amplitude of twitches.     

Modulation of the contractile activity of the fast and slow twitch rat muscle during continuous stimulation

The fast- and slow-twitch muscles were tested with single pulses in the course of unfused tetanus formation. The tetanus decreased differences in contractile parameters of the test-twitch contractions and, after continuous stimulation, eliminated them altogether.     

Myosin isoform transitions in regeneration of fast and slow muscles during postnatal development of the rat

Regeneration of rat fast (gastrocnemius medialis) and slow (soleus) muscles was examined after degeneration of myofibers had been achieved by injection of cardiotoxin into the hindleg during the first week after birth. Myogenesis in the regenerating muscles was compared to postnatal myogenesis in the contralateral and in control muscles. Synthesis of embryonic and neonatal myosin isoforms was initiated 3 days after injury. These forms were gradually replaced by the intermediate and fast adult isoforms (type II fiber myosins), whose synthesis followed the same curve in regenerating, contralateral, and control muscles. In contrast, synthesis of the slow myosin isoform (type I fiber myosin) was greatly delayed in injured muscles, but eventually became equal to its synthesis in contralateral and control muscles. It therefore appears that synthesis of type II fiber myosins is similarly regulated, probably by thyroid hormone, in developing regenerating and normal muscles, while synthesis of type I fiber myosin depends on other factor(s).