Comparative analysis of structural and functional characteristics of soleus muscle in rats and Mongolian gerbils during gravitational unloading of various duration

A comparative investigation of the dynamics of contractile properties of the whole soleus muscle and its fibers during 3- and 12-day-long hind limb suspension of Wistar rats and Mongolian gerbils (Meriones unguiculatus) has been performed. The data obtained indicate that the structural and functional changes caused by hypogravity in gerbils are slowed down compared with rats. A very intensive drop in water containment in gerbils was found, which can cause shifts in the ionic strength of the intracellular space of the muscle fiber. As a result, the photolytic activity of different enzymes may change, which can induce a less pronounced reduction in Z-disc and M-line stiffness and contractile capabilities in gerbils compared to rats.     

Contractile properties and myosin expression in rats born and reared in hypergravity

The effects of hypergravity (HG) on soleus and plantaris muscles were studied in Long Evans rats aged 100 days, born and reared in 2-g conditions (HG group). The morphological and contractile properties and the myosin heavy chain (MHC) content were examined in whole muscles and compared with terrestrial control (Cont) age-paired rats. The growth of HG rats was slowed compared with Cont rats. A decrease in absolute muscle weight was observed. An increase in fiber cross-sectional area/muscle wet weight was demonstrated, associated with an increase in relative maximal tension. The soleus muscle changed into a slower type both in contractile parameters and in MHC content, since HG soleus contained only the MHC I isoform. The HG plantaris muscle presented a faster contractile behavior. Moreover, the diversity of hybrid fiber types expressing multiple MHC isoforms (including MHC IIB and MHC IIX isoforms) was increased in plantaris muscle after HG. Thus the HG environment appears as an important inductor of muscular plasticity both in slow and fast muscle types.     

Changes in isoform composition,structure, and functional properties of titin from mongolian gerbil (<Emphasis Type="Italic">Meriones unguiculatus</Emphasis>) cardiac muscle after space flight

Changes in isoform composition, secondary structure, and titin phosphorylation in Mongolian gerbil (Meriones unguiculatus) cardiac muscle were studied after 12-day-long space flight onboard the Russian spacecraft Foton-M3. The effect of titin on the actin-activated myosin ATPase activity at pCa 7.5 and 4.6 was also studied. Almost twofold increase in titin long N2BA isoform content relative to that of short N2B isoform was found on electrophoregrams of cardiac muscle left ventricle of the flight group gerbils. Differences in secondary structure of titin isolated from cardiac muscle of control and flight groups of gerbils were found. An increase in phosphorylation (1.30–1.35-fold) of titin of cardiac muscle of the flight group gerbils was found. A decrease in activating effect of titin of cardiac muscle of the flight group gerbils on actomyosin ATPase activity in vitro was also found. The observed changes are discussed in the context of M. unguiculatus cardiac muscle adaptation to conditions of weightlessness.     

Role of NO-synthase in regulation of protein metabolism of stretched rat m. soleus muscle during functional unloading

Gravitational unloading causes atrophy of muscle fibers and can lead to destruction of cytoskeletal and contractile proteins. Along with the atrophic changes, unloaded muscle frequently demonstrates significant shifts in the ratio of muscle fibers expressing fast and slow myosin heavy chain isoforms. Stretching of the m. soleus during hindlimb suspension prevents its atrophy. We supposed that neuronal NO-synthase (NOS) (which is attached to membrane dystrophin-sarcoglycan complex) can contribute to maintenance of protein metabolism in the muscle and prevent its atrophy when m. soleus is stretched. To test this hypothesis, we used Wistar rats (56 animals) in experiments with hindlimb suspension during 14 days. The group of hindlimb suspended rats with stretched m. soleus was injected with L-NAME to block NOS activity. We found that m. soleus mass and its protein content in hindlimb-suspended rats with stretched m. soleus were preserved due to prevention of protein degradation. NOS is involved in maintenance of expression of some muscle proteins. Proliferation of satellite cells in stretched m. soleus may be due to nNOS activity, but maintenance of muscle mass upon stretching is regulated not by NOS alone.     

Dynamics of calcium ions accumulation and changes of isoforms of sarcoplasmic reticulum Ca-ATPase (SERCA) in soleus muscle fibers of rats and Mongolian gerbils under gravitational unloading of various duration

The concentration of calcium ions in soleus muscle fibers in Mongolian gerbils and rats has been shown to increase for the first day of gravitational load by 4.5 and 2.8 times, respectively, compared to the control. This increase is preserved for 3 days, while, after 12 days, it decreases, but remains above the control level. The resting calcium level in the control in gerbils is lower than in rats and, as a consequence, its change for the first day of unloading is greater. It is possible that this leads to earlier changes in the muscle fiber isoform composition in gerbils; a statistically significant shift in the ratio of fibers that contain fast and slow calcium pumps towards pumping faster is noted as early as the first day, while that of fibers that express the corresponding isoforms of myosin heavy chains (MHCs) is observed after 3 days of functional unloading. In rats, similar changes are revealed as late as on the 7th day. After 12 days, in both species, a tendency to return to the control level is observed that is more pronounced in gerbil.     

Adaptation of rat skeletal muscle to creatine depletion: AMP deaminase and AMP deamination.

AMP deaminase catalyzes deamination of the AMP formed in contracting muscles to inosine 5'-monophosphate (IMP). Slow-twitch muscle has only approximately 30% as high a level of AMP deaminase activity as fast-twitch muscle in the rat, and rates of IMP formation during intense contractile activity are much lower in slow-twitch muscle. We found that feeding the creatine analogue beta-guanidinopropionic acid (beta-GPA) to rats, which results in creatine depletion, causes a large decrease in muscle AMP deaminase. This adaptation was used to evaluate the role of AMP deaminase activity level in accounting for differences in IMP production in slow-twitch and fast-twitch muscles. beta-GPA feeding for 3 wk lowered AMP deaminase activity in fast-twitch epitrochlearis muscle to a level similar to that found in the normal slow-twitch soleus muscle but had no effect on the magnitude of the increase in IMP in response to intense contractile activity. Despite a similar decrease in ATP in the normal soleus and the epitrochlearis from beta-GPA-fed rats, the increase in IMP was only approximately 30% as great in the soleus in response to intense contractile activity. These results demonstrate that the accumulation of less IMP in slow- compared with fast-twitch skeletal muscle during contractile activity is not due to the lower level of AMP deaminase in slow-twitch muscle.     

The effect of two episodes of denervation and reinnervation on skeletal muscle contractile function.

Sensory or motor "baby-sitting" has been proposed as a clinical strategy to preserve muscle integrity if motion-specific axons must regenerate over a long distance to reach denervated target muscles. Denervated muscles are innervated temporarily by using axons from nearby sensory or motor nerves. After motion specific motor axons have reached the target, the baby-sitter nerve is severed and motion-specific axons are directed to the target. Although this strategy minimizes denervation time, the requisite second episode of denervation and reinnervation might be deleterious to muscle contractile function. This study was designed to test the hypothesis that two sequential episodes of skeletal muscle denervation and reinnervation result in greater force and power deficits than a single peripheral nerve injury and repair. Adult Lewis rats underwent either transection and epineurial repair or sham exposure of the left peroneal nerve. After a 4-month recovery period, the contractile properties of the extensor digitorum longus muscle of the sham exposure group (control, n = 9) and one of the nerve division and repair groups (repair group 1, n = 9) were evaluated with measurements of the maximum tetanic isometric force, peak power, and maximal sustained power. A third group of rats underwent a second cycle of nerve division and repair (repair group 2, n = 9) at this same time point. Four months postoperatively, contractile properties of the extensor digitorum longus muscles were evaluated. Maximum tetanic isometric force and peak power were significantly reduced in repair group 2 rats as compared with repair group 1 and control rats. Maximal sustained power was not significantly different between the groups. These data support our working hypothesis that skeletal muscle contractile function is adversely affected by two cycles of denervation and reinnervation as compared with a single episode of nerve division and repair.     

The effect of ovariectomy on the contractile response of the rat isolated detrusor muscle and urethra

Contractile responses induced by carbachol on the detrusor muscle and by noradrenaline on the isolated urethra were compared between ovariectomized rats pretreated with estradiol (50 μg/animal s.c. twice daily for five days), untreated ovariectomized rats and intact animals. In the detrusor muscle, contractions induced by 30μM carbachol, when normalized with respect to KCl 100 mM-induced contraction, were similar for the three groups. Furthermore, contractions induced by 100 μM noradrenaline in the isolated urethra were not significatively different between groups. However, the pD₂ value for noradrenaline was greater in urethral tissue from ovariectomized rats compared with ovariectomized -estrogen treated and control rats. A similar result was found for pD₂ values for carbachol-induced contractions on the detrusor muscle. These results suggest that ovariectomy increases the sensitivity of the urinary bladder and urethra to the contractile effects of carbachol and noradrenaline, respectively and that this effect is reversed by in vivo estrogen pretreatment.     

Effects of alpha-chlorohydrin and gonadectomy on the adenohypophysial cells of male rats and gerbils

The cytological changes occurring in the gonadotropic cells of the anterior lobe of the pituitary in 30 male rats and 30 male gerbils after administration of alpha-chlorohydrin were compared with those occurring following bilateral gonadectomy. A decline in the weights of testes and accessory sex glands and inhibited spermatogenesis were noted in rats and gerbils following alpha-chlorohydrin administration. Alpha-cholorohydrin changed the appearance of the delta-basilphils, cell cytoplasm showed fine granulation and vacuolization, and castration vacuoles appeared in many delta-basiphils of the anteroir lobe of the pituitary. The compound brought about transient changes resembling those of castration in the anterior lobe of the pituitary of male rats and gerbils. In gerbils, there was also a marked decrease in the number of acidophils. The results show that alpha-chlorohydrin exerts its effects on androgen-dependent structures, e.g., seminal vesicles, ventral prostrate, epididymides, and perineal complex.     

Regional differences in myosin heavy chain isoform expression and maximal shortening velocity of the rat vaginal wall smooth muscle

Contractility of the proximal and distal vaginal wall smooth muscle may play distinct roles in the female sexual response and pelvic support. The goal of this study was to determine whether differences in contractile characteristics of smooth muscle from these regions reside in differences in the expression of isoforms of myosin, the molecular motor for muscle contraction. Adult female Sprague-Dawley rats were killed on the day of estrus, and the vagina was dissected into proximal and distal segments. The Vmax at peak force was greater for tissue strips of the proximal vagina compared with that of distal (P < 0.01), although, at steady state, the Vmax for the muscle strips from the two regions was not different. Furthermore, at steady state, muscle stress was higher (P < 0.001) for distal vaginal strips (n = 5). Consistent with the high Vmax for the proximal vaginal strips, RT-PCR results revealed a higher %SM-B (P < 0.001) in the proximal vagina. A greater expression of SM-B protein (P < 0.001) was also detected by Western blotting (n = 4). Interestingly, there was no regional difference noted in SM-1/SM-2 isoforms (n = 6). The proximal vagina had a higher expression of myosin heavy chain protein (P < 0.01) and a greater percentage of smooth muscle bundles (P < 0.001). The results of this study are the first demonstration of a regional heterogeneity in Vmax and myosin isoform distribution in the vagina wall smooth muscle and confirm that the proximal vaginal smooth muscle exhibits phasic contractile characteristics compared with the distal vaginal smooth muscle, which is tonic.     

Changes in rat soleus muscle phenotype consecutive to a growth in hypergravity followed by normogravity

It has been demonstrated that a long-term stay in hypergravity (HG: 2G) modified the phenotype and the contractile properties of rat soleus muscle. The ability of this muscle to contract was drastically reduced, which is a sign of anticipated aging. Consequently, our aim was to determine whether rats conceived, born, and reared in hypergravity showed adaptative capacities in normogravity (NG: 1G). This study was performed on rats divided into two series: the first was reared in HG until 100 days and was submitted to normogravity until 115 to 220 postnatal days (HG-NG rats); the second was made up of age paired groups reared in normogravity (NG rats). The contractile, morphological, and phenotypical properties of soleus muscle were studied. Our results showed that the NG rats were characterized by coexpressions of slow and fast myosin, respectively, 76.5 and 23.5% at 115 days. During their postnatal maturation, the fast isoform was gradually replaced by slow myosin. At 220 days, the relative proportions were respectively 91.05% and 8.95%. From 115 to 220 days, the HG-NG rats expressed 100% of slow myosin isoform and they presented a slower contractile behavior compared with their age-matched groups; at 115 days, the whole muscle contraction time was increased by 35%, and by 15%, at 220 days. Our study underlined the importance of gravity in the muscular development and suggested the existence of critical periods in muscle phenotype installation.     

Effects of endurance exercise-training on single-fiber contractile properties of insulin-treated streptozotocin-induced diabetic rats.

The purpose of this study was to characterize the contractile properties of individual skinned muscle fibers from insulin-treated streptozotocin-induced diabetic rats after an endurance exercise training program. We hypothesized that single-fiber contractile function would decrease in the diabetic sedentary rats and that endurance exercise would preserve the function. In the study, 28 rats were assigned to either a nondiabetic sedentary, a nondiabetic exercise, a diabetic sedentary, or a diabetic exercise group. Rats in the diabetic groups received subcutaneous intermediate-lasting insulin daily. The exercise-trained rats ran on a treadmill at a moderate intensity for 60 min, five times per week. After 12 wk, the extensor digitorum longus and soleus muscles were dissected. Single-fiber diameter, Ca(2+)-activated peak force, specific tension, activation threshold, and pCa(50) as well as the myosin heavy chain isoform expression (MHC) were determined. We found that in MHC type II fibers from extensor digitorum longus muscle, diameters were significantly smaller from diabetic sedentary rats compared with nondiabetic sedentary rats (P < 0.001). Among the nondiabetic rats, fiber diameters were smaller with exercise (P = 0.038). The absolute force-generating capacity of single fibers was lower in muscles from diabetic rats. There was greater specific tension (force normalized to cross-sectional area) by fibers from the rats that followed an endurance exercise program compared with sedentary. From the results, we conclude that alterations in the properties of contractile proteins are not implicated in the decrease in strength associated with diabetes and that endurance-exercise training does not prevent or increase muscle weakness in diabetic rats.     

Dietary Fat Influences the Expression of Contractile and Metabolic Genes in Rat Skeletal Muscle

Dietary fat plays a major role in obesity, lipid metabolism, and cardiovascular diseases. To determine whether the intake of different types of dietary fats affect the muscle fiber types that govern the metabolic and contractile properties of the skeletal muscle, we fed male Wistar rats with a 15% fat diet derived from different fat sources. Diets composed of soybean oil (n-6 polyunsaturated fatty acids (PUFA)-rich), fish oil (n-3 PUFA-rich), or lard (low in PUFAs) were administered to the rats for 4 weeks. Myosin heavy chain (MyHC) isoforms were used as biomarkers to delineate the skeletal muscle fiber types. Compared with soybean oil intake, fish oil intake showed significantly lower levels of the fast-type MyHC2B and higher levels of the intermediate-type MyHC2X composition in the extensor digitorum longus (EDL) muscle, which is a fast-type dominant muscle. Concomitantly, MyHC2X mRNA levels in fish oil-fed rats were significantly higher than those observed in the soybean oil-fed rats. The MyHC isoform composition in the lard-fed rats was an intermediate between that of the fish oil and soybean oil-fed rats. Mitochondrial uncoupling protein 3, pyruvate dehydrogenase kinase 4, and porin mRNA showed significantly upregulated levels in the EDL of fish oil-fed rats compared to those observed in soybean oil-fed and lard-fed rats, implying an activation of oxidative metabolism. In contrast, no changes in the composition of MyHC isoforms was observed in the soleus muscle, which is a slow-type dominant muscle. Fatty acid composition in the serum and the muscle was significantly influenced by the type of dietary fat consumed. In conclusion, dietary fat affects the expression of genes related to the contractile and metabolic properties in the fast-type dominant skeletal muscle, where the activation of oxidative metabolism is more pronounced after fish oil intake than that after soybean oil intake.     

The role of extracellular calcium in pregnancy-induced attenuation of phenylephrine contraction in rat aorta with functional endothelium

The effect of pregnancy on the supply of calcium ions for the contractile responses of rat aortic rings to phenylephrine was investigated. The contractility of intact aortic rings from pregnant rats, compared with that of similar rings from non-pregnant rats, to phenylephrine and potassium chloride was significantly decreased. Contractions of rings from non-pregnant rats, pretreated with phenylephrine or potassium chloride, in response to calcium chloride were greater than those of similarly treated rings from pregnant rats. When the concentration of calcium chloride in the medium bathing the rings was reduced to 0.8 mmol·l^-1, the contractile response to phenylephrine was significantly (P<0.005) inhibited in rings from both pregnant and non-pregnant rats but to a greater extent in rings from non-pregnant rats. Contractions of aortic rings from pregnant rats in response to phenylephrine in calcium-free medium were similar to those of rings from non-pregnant rats, suggesting equal dependence on calcium from intracellular stores. The results suggest that pregnancy decreased the response to calcium influx into the aortic smooth muscle cells through both receptor-and voltage-operated calcium entry pathways. Since de-endothelialisation reversed the pregnancy-induced diminished contraction to phenylephrine, it is likely that pregnancy interferred with contractions induced by activation of receptors with phenylephrine through enhanced production of endothelium-derived relaxing factor(s).Abbreviations EC₅₀ concentration of drug producing 50% contraction - EDCF endothelium-derived contraction factor - EGTA ethyleneglycol-bis (-aminoethyl ether)-NN tetraacetic acid - PSS physiological salt solution - VSM vascular smooth muscle     

Effect of streptozotocin diabetes on motor and inhibitory transmission in rat anococcygeus.

The effect of streptozotocin diabetes of 4-week duration on the adrenergic motor transmission and on the nonadrenergic, noncholinergic, inhibitory transmission in the rat anococcygeus was investigated by recording contractile and relaxant activity of isolated muscle preparations taken from diabetic and age-matched control animals. The neurogenic contractile responses to electrical field stimulation were significantly reduced in the preparations from diabetic rats. The inhibitory transmission remained unaffected in the diabetic rats. Concentration--response curves showed no change in sensitivity of the diabetic anococcygei to noradrenaline. The maximum tension generated was also similar in preparations from diabetic and nondiabetic animals. The contractile responses to electrical field stimulation were significantly greater in preparations from diabetic rats treated for 4 weeks with either sorbinil (20 mg.kg-1.day-1 orally) or myo-inositol (667 mg.kg-1.day-1 orally) when compared with the untreated diabetic controls; the sensitivity to noradrenaline was identical in all three groups. It is concluded that streptozotocin diabetes causes a significant reduction of adrenergic contractile responses of the anococcygeus to electrical field stimulation by a prejunctional mechanism, and the reduction can be prevented by treating the animals with the aldose reductase inhibitor sorbinil or with myo-inositol.     

Work partitioning of transversally loaded muscle: experimentation and simulation

Skeletal muscles are surrounded by other muscles, connective tissue and bones, which may transfer transversal forces to the muscle belly. Simple Hill-type muscle models do not consider transversal forces. Thus, the aim of this study was to examine and model the influence of transversal muscle loading on contraction dynamics, e.g. on the rate of force development and on the maximum isometric muscle force (F_im). Isometric experiments with and without transversal muscle loading were conducted on rat muscles. The muscles were loaded (1.3 N cm^? 2) by a custom-made plunger which was able to move in transversal direction. Then the muscle was fully stimulated, the isometric force was measured at the distal tendon and the movement of the plunger was captured with a high-speed camera. The interaction between the muscle and the transversal load was modelled based on energy balance between the (1) work done by the contractile component (CC) and (2) the work done to lift the load, to stretch the series elastic structures and to deform the muscle. Compared with the unloaded contraction, the force rate was reduced by about 25% and F_im was reduced by 5% both in the experiment and in the simulation. The reduction in F_im resulted from using part of the work done by the CC to lift the load and deform the muscle. The response of the muscle to transversal loading opens a window into the interdependence of contractile and deformation work, which can be used to specify and validate 3D muscle models.     

Sexual dimorphism in histological characteristics and contractility of the iliofibularis muscle in the lizard Sceloporus torquatus

The iliofibularis is a hindlimb muscle used in lizard locomotion that is composed of at least three types of fibres: fast‐twitch‐glycolytic (FG), fast‐twitch‐oxidative‐glycolytic fibre (FOG) and slow‐twitch‐oxidative (SO). The striated skeletal muscle is a highly plastic tissue undergoing phenotypic change in response to activity. The lizard Sceloporus torquatus has sexual differences associated with microhabitat use, which can be reflected in the physiology and anatomy of the muscle, and thus, in our study, we analysed the morphological and contractile characteristics of the iliofibularis muscle (IF) of S. torquatus males and females. We found a larger prevalence of FOG compared with FG and SO fibres in the muscle of both sexes. We also found that males show larger areas of the three types of fibres, develop greater strength but also faster fatigue than females, suggesting that strength is a key functional feature that enables males to perform faster movements (but for shorter periods), associated with the demands of territoriality.     

The effects of neuropeptide Y on skeletal muscle contractile properties in streptozotocin diabetic rats

Diabetes induces changes in the structural, biochemical, electrical, and contractile properties of skeletal muscles. Neuropeptide Y (NPY) administered locally can induce angiogenesis in a rat ischemic limb model and restore the contractile function of the ischemic muscle. The effects of NPY on the contractile characteristics of limb skeletal muscles were examined in streptozotocin-induced diabetic rats. Rats were treated with sham pellets (control groups) or NPY-containing pellets (1 mg of NPY/pellet, 14 days releasing time) administered locally to the rat hind limb 2 months after induction of diabetes. Contractile properties and fatigability of the slow-twitch soleus and fast-twitch gastrocnemius medials muscle were compared in control (sham), control NPY, diabetic (sham), and diabetic NPY groups. In order to induce fatigue trains of repetitive tetanic stimulation were used (600 ms/1 s simulation-rest cycle per train, 112 trains at an 85-Hz fusion frequency). Two months of untreated diabetes significantly prolonged soleus contraction and slowed its relaxation, but had minimal effects on soleus tension. NPY ameliorated the diabetic effects on soleus speed-related contractile properties, restoring its contraction and relaxation times. Diabetes significantly reduced gastrocnemius medials tetanic tension, leaving its contractile characteristics mostly unaffected. NPY partially restored gastrocnemius tetanic tension production capacity. Diabetes significantly increased fatigability of both muscles, which was partially restored by NPY, as evidenced by restored endurance of soleus muscle. The results suggest that NPY administered locally tends to normalize muscle performance and improve fatigue resistance of skeletal muscles in streptozotocin diabetes. Further examination is needed to establish the mechanisms of local NPY action on muscle contractile properties in streptozotocin-induced diabetes.     

长爪沙鼠血清雌性激素的比较研究

目的测定长爪沙鼠、NIH小鼠和SD大鼠的血清雌二醇(E2)和孕酮(P)水平,为研究长爪沙鼠的生殖和胚胎工程提供基础资料。方法用放射免疫分析法测定上述动物生产前后血清雌二醇(E2)和孕酮(P)水平,进行统计学处理和分析。结果不同阶段雌性沙鼠E2值差异无显著性(P>0.05),P值差异有显著性(P<0.01);E2值比较,处女期沙鼠与同期NIH和SD差异有显著性(P<0.01),而在经产期的动物间水平接近(P>0.05);P值比较,处女期沙鼠与NIH接近,与SD差异有显著性(P<0.01);而经产期沙鼠在三种动物中是最高的(P<0.01)。结论长爪沙鼠血清E2、P的含量具种属特异性,并随动物的生理发育时期而变化。