AEROBIC EXERCISE TRAINING CORRECTS CAPILLARY RAREFACTION AND ALTERATIONS IN PROPORTIONS OF THE MUSCLE FIBERS TYPES IN SPONTANEOUSLY HYPERTENSIVE RATS

Aerobic exercise training (ET) has been established as an important non-pharmacological treatment of hypertension, since it decreases blood pressure. Studies show that the skeletal muscle abnormalities in hypertension are directly associated with capillary rarefaction, higher percentage of fast-twitch fibers (type II) with glycolytic metabolism predominance and increased muscular fatigue. However, little is known about these parameters in hypertension induced by ET. We hypothesized that ET corrects capillary rarefaction, potentially contributing to the restoration of the proportion of muscle fiber types and metabolic proprieties. Twelve-week old Spontaneously Hypertensive Rats (SHR, n=14) and Wistar Kyoto rats (WKY, n=14) were randomly assigned into 4 groups: SHR, trained SHR (SHR-T), WKY and trained WKY (WKY-T). As expected, ten weeks of ET was effective in reducing blood pressure in SHR-T group. In addition, we analyzed the main markers of ET. Resting bradycardia, increase of exercise tolerance, peak oxygen uptake and citrate synthase enzyme activity in trained groups (WKY-T and SHR-T) showed that the aerobic condition was achieved. ET also corrected the skeletal muscle capillary rarefaction in SHR-T. In parallel, we observed reduction in percentage of type IIA and IIX fibers and simultaneous augmented percentage of type I fibers induced by ET in hypertension. These data suggest that ET prevented changes in soleus fiber type composition in SHR, since angiogenesis and oxidative enzyme activity increased are important adaptations of ET, acting in the maintenance of muscle oxidative metabolism and fiber profile.

Early effects of carbachol on the morphology of motor endplates of mammalian skeletal muscle fibers

Long-term disturbance of the calcium homeostasis of motor endplates (MEPs) causes necrosis of muscle fibers. The onset of morphological changes in response to this disturbance, particularly in relation to the fiber type, is presently unknown. Omohyoid muscles of mice were incubated for 1-30 minutes in 0.1 mM carbachol, an acetylcholine agonist that causes an inward calcium current. In these muscles, the structural changes of the sarcomeres and the MEP sarcoplasm were evaluated at the light- and electron-microscopic level. Predominantly in type I fibers, carbachol incubation resulted in strong contractures of the sarcomeres underlying the MEPs. Owing to these contractures, the usual beret-like form of the MEP-associated sarcoplasm was deformed into a mushroom-like body. Consequently, the squeezed MEPs partially overlapped the adjacent muscle fiber segments. There are no signs of contractures below the MEPs if muscles were incubated in carbachol in calcium-free Tyrode's solution. Carbachol induced inward calcium current and produced fiber-type-specific contractures. This finding points to differences in the handling of calcium in MEPs. Possible mechanisms for these fiber-type-specific differences caused by carbachol-induced calcium entry are assessed.

Effects of Estrogen on Muscle Damage in Response to an Acute Resistance Exercise Protocol

Creatine Kinase (CK) is used as a measure of exercise-induced muscle membrane damage. During acute eccentric (muscle lengthening) exercise, muscle sarcolemma, sarcoplasmic reticulum, and Z-lines are damaged, thus causing muscle proteins and enzymes to leak into the interstitial fluid. Strenuous eccentric exercise produces an elevation of oxygen free radicals, which further increases muscle damage. Muscle soreness and fatigue can be attributed to this membrane damage. Estradiol, however, may preserve membrane stability post-exercise (Brancaccio, Maffulli, & Limongelli, 2007; Carter, Dobridge, & Hackney, 2001; Tiidus, 2001). Because estradiol has a similar structure to Vitamin E, which is known to have antioxidant properties, and both are known to affect membrane structure, researchers have proposed that estrogen acts as an antioxidant to provide a protective effect on the post-exercise muscle of women (Sandoval & Matt, 2002). As a result, it has been postulated that muscles in women incur less damage in response to an acute strenuous exercise as compared to men. PURPOSE: To determine if circulating estrogen concentrations are related to muscle damage, as measured by creatine kinase activity and to determine gender differences in creatine kinase as a marker of muscle damage in response to an acute heavy resistance exercise protocol. METHODS: 7 healthy, resistance-trained, eumenhorrheic women (23±3 y, 169±9.1 cm, 66.4±10.5 kg) and 8 healthy, resistance-trained men (25±5 y, 178±6.7 cm, 82.3±9.33 kg) volunteered to participate in the study. Subjects performed an Acute Resistance Exercise Test (ARET) consisting of 6 sets of 5 repetitions Smith machine squats at 90% of their previously determined 1-RM. Blood samples were taken pre-, mid-, post-, 1 hour post-, 6 hours post-, and 24 hours post-exercise. Samples were stored at -80ºC until analyzed. Serum creatine kinase was measured using an assay kit from Genzyme (Framingham, MA). Serum estradiol was measured by an ELISA from GenWay (San Diego, CA). Estradiol b-receptor presence on granulocytes was measured via flow cytometry using primary antibodies from Abcam (Cambridge, MA) and PeCy7 antibodies (secondary) from Santa Cruz (Santa Cruz, CA). RESULTS: No significant correlations between estrogen and CK response were found after an acute resistant exercise protocol. Moreover, no significant change in estradiol receptors were expressed on granulocytes after exercise. Creatine Kinase response, however, differed significantly between genders. Men had higher resting CK concentrations throughout all time points. Creatine Kinase response increased significantly after exercise in both men and women (p=0.008, F=9.798). Men had a significantly higher CK response at 24 hours post exercise than women. A significant condition/sex/time interaction was exhibited in CK response (p=0.02, F=4.547). Perceived general soreness presented a significant condition, sex interaction (p=0.01, F=9.532). DISCUSSION: Although no estradiol and CK response correlations were found in response to exercise, a significant difference in creatine kinase activity was present between men and women. This discrepancy of our results and findings in the literature may be due to the high variability between subjects in creatine kinase activity as well as estrogen concentrations. The lack of significance in change of estradiol receptor expression on granulocytes in response to exercise may be due to intracellular estradiol receptor staining and non-specific gating for granulocytes rather than additional staining for neutrophil markers. Because neutrophils are the initial cells present in the inflammatory response after strenuous exercise, staining for estrogen receptors on this cell type may allow for a better understanding of the effect of estrogen and its hypothesized protective effect against muscle damage. Furthermore, the mechanism of action may include estradiol receptor expression on the muscle fiber itself may play a role in the protective effects of estradiol rather than or in addition to expression on neutrophils. We have shown here that gender differences occur in CK activity as a marker of muscle damage in response to strenuous eccentric exercise, but may not be the result of estradiol concentration or estradiol receptor expression on granulocytes. Other variables should be examined in order to determine the mechanism involved in the difference in creatine kinase as a marker of muscle damage between men and women after heavy resistance exercise.

Modulation of replicative senescence of skeletal muscle satellite cells by insulin -like growth factor-I (IGF-I)

Growth and regeneration of postnatal skeletal muscle requires a population of mononuclear myogenic cells, called satellite cells to add/replace myonuclei, which are postmitotic. Wedged between the sarcolemma and the basal lamina of the skeletal muscle fiber, these cells function as the stem cells of mature muscle fibers. Like other normal diploid cells, satellite cells undergo cellular senescence. Investigations of aging in both rodents and humans have shown that satellite cell self-renewal capacity decreases with advanced age. As a consequence, this could be a potential reason for the characteristically observed age-associated loss in skeletal muscle mass (sarcopenia). This provided the rationale that any intervention that can further increase the proliferative capacity of these cells should potentially be able to either delay, or even prevent sarcopenia. ^ Using clonogenicity assays to determine a cell's proliferation potential, these studies have shown that IGF-I enhances the doubling potential of satellite cells from aged rodents. Using a transgenic model, where the mice express the IGF-I transgene specifically in their striated muscles, some of the underlying biochemical mechanisms for the observed increase in replicative life span were delineated. These studies have revealed that IGF-I activates the PI3/Akt pathway to mediate downregulation of p27KIP1, which consequently is associated with an increase in cyclin E-cdk2 kinase activity, phosphorylation of pRb, and upregulation of cyclin A protein. However, the beneficial effects of IGF-I on satellite cell proliferative potential appears to be limited as chronic overexpression of IGF-I in skeletal muscles did not protect against sarcopenia in 18-mo old mice, and was associated with an exhaustion of satellite cell replicative reserves. ^ These results have shown that replicative senescence can be modulated by environmental factors using skeletal muscle satellite cells as a model system. A better understanding of the molecular basis for enhancement of proliferative capacity by IGF-I will provide a rational basis for developing more effective counter-measures against physical frailty. However, the implications of these studies are that these beneficial effects of enhanced proliferative potential by IGF-I may only be over a short-term period, and other alternative approaches may need to be considered. ^

Voltage dependence of the pattern and frequency of discrete Ca2+ release events after brief repriming in frog skeletal muscle

Applying a brief repolarizing pre-pulse to a depolarized frog skeletal muscle fiber restores a small fraction of the transverse tubule membrane voltage sensors from the inactivated state. During a subsequent depolarizing test pulse we detected brief, highly localized elevations of myoplasmic Ca2+ concentration (Ca2+ “sparks”) initiated by restored voltage sensors in individual triads at all test pulse voltages. The latency histogram of these events gives the gating pattern of the sarcoplasmic reticulum (SR) calcium release channels controlled by the restored voltage sensors. Both event frequency and clustering of events near the start of the test pulse increase with test pulse depolarization. The macroscopic SR calcium release waveform, obtained from the spark latency histogram and the estimated open time of the channel or channels underlying a spark, exhibits an early peak and rapid marked decline during large depolarizations. For smaller depolarizations, the release waveform exhibits a smaller peak and a slower decline. However, the mean use time and mean amplitude of the individual sparks are quite similar at all test depolarizations and at all times during a given depolarization, indicating that the channel open times and conductances underlying sparks are essentially independent of voltage. Thus, the voltage dependence of SR Ca2+ release is due to changes in the frequency and pattern of occurrence of individual, voltage-independent, discrete release events.

Regulation of Myosin Heavy Chain Expression during Rat Skeletal Muscle Development In Vitro

Signals that determine fast- and slow-twitch phenotypes of skeletal muscle fibers are thought to stem from depolarization, with concomitant contraction and activation of calcium-dependent pathways. We examined the roles of contraction and activation of calcineurin (CN) in regulation of slow and fast myosin heavy chain (MHC) protein expression during muscle fiber formation in vitro. Myotubes formed from embryonic day 21 rat myoblasts contracted spontaneously, and ∼10% expressed slow MHC after 12 d in culture, as seen by immunofluorescent staining. Transfection with a constitutively active form of calcineurin (CN*) increased slow MHC by 2.5-fold as determined by Western blot. This effect was attenuated 35% by treatment with tetrodotoxin and 90% by administration of the selective inhibitor of CN, cyclosporin A. Conversely, cyclosporin A alone increased fast MHC by twofold. Cotransfection with VIVIT, a peptide that selectively inhibits calcineurin-induced activation of the nuclear factor of activated T-cells, blocked the effect of CN* on slow MHC by 70% but had no effect on fast MHC. The results suggest that contractile activity-dependent expression of slow MHC is mediated largely through the CN–nuclear factor of activated T-cells pathway, whereas suppression of fast MHC expression may be independent of nuclear factor of activated T-cells.

Zebrafish as a model for caveolin-associated muscle disease; caveolin-3 is required for myofibril organization and muscle cell patterning

Caveolae are an abundant feature of many animal cells. However, the exact function of caveolae remains unclear. We have used the zebrafish, Danio rerio, as a system to understand caveolae function focusing on the muscle-specific caveolar protein, caveolin-3 (Cav3). We have identified caveolin-1 (alpha and beta), caveolin-2 and Cav3 in the zebrafish. Zebrafish Cav3 has 72% identity to human CAV3, and the amino acids altered in human muscle diseases are conserved in the zebrafish protein. During embryonic development, cav3 expression is apparent by early segmentation stages in the first differentiating muscle precursors, the adaxial cells and slightly later in the notochord. cav3 expression appears in the somites during mid-segmentation stages and then later in the pectoral fins and facial muscles. Cav3 and caveolae are located along the entire sarcolemma of late stage embryonic muscle fibers, whereas beta-dystroglycan is restricted to the muscle fiber ends. Down-regulation of Cav3 expression causes gross muscle abnormalities and uncoordinated movement. Ultrastructural analysis of isolated muscle fibers reveals defects in myoblast fusion and disorganized myofibril and membrane systems. Expression of the zebrafish equivalent to a human muscular dystrophy mutant, CAV3P104L, causes severe disruption of muscle differentiation. In addition, knockdown of Cav3 resulted in a dramatic up-regulation of eng1a expression resulting in an increase in the number of muscle pioneer-like cells adjacent to the notochord. These studies provide new insights into the role of Cav3 in muscle development and demonstrate its requirement for correct intracellular organization and myoblast fusion.

Selection for muscle fat content and triploidy affect flesh quality in pan-size rainbow trout, Oncorhynchus mykiss

A lean muscle line (L) and a fat muscle line (F) of rainbow trout were established (Quillet et al., 2005) by a two-way selection for muscle lipid content performed on pan-size rainbow trout using a non-destructive measurement of muscle lipid content (Distell Fish Fat Meter®). The aim of the present study was to evaluate the consequences of this selective breeding on flesh quality of pan size (290 g) diploid and triploid trout after three generations of selection. Instrumental evaluations of fillet color and pH measurement were performed at slaughter. Flesh color, pH, dry matter content and mechanical resistance were measured at 48 h and 96 h postmortem on raw and cooked flesh, respectively. A sensorial profile analysis was performed on cooked fillets. Fillets from the selected fatty muscle line (F) had a higher dry matter content and were more colorful for both raw and cooked fillets. Mechanical evaluation indicated a tendency of raw flesh from F fish to be less firm, but this was not confirmed after cooking, neither instrumentally or by sensory analysis. The sensory analysis revealed higher fat loss, higher intensity of flavor of cooked potato, higher exudation, higher moisture content and a more fatty film left on the tongue for flesh from F fish. Triploid fish had mechanically softer raw and cooked fillets, but the difference was not perceived by the sensorial panel. The sensorial evaluation also revealed a lower global intensity of odor, more exudation and a higher moisture content in the fillets from triploid fish. These differences in quality parameters among groups of fish were associated with larger white muscle fibers in F fish and in triploid fish. The data provide additional information about the relationship between muscle fat content, muscle cellularity and flesh quality.

Genetic Aspects Of Athletic Performance: The African Runners Phenomenon.

The current dominance of African runners in long-distance running is an intriguing phenomenon that highlights the close relationship between genetics and physical performance. Many factors in the interesting interaction between genotype and phenotype (eg, high cardiorespiratory fitness, higher hemoglobin concentration, good metabolic efficiency, muscle fiber composition, enzyme profile, diet, altitude training, and psychological aspects) have been proposed in the attempt to explain the extraordinary success of these runners. Increasing evidence shows that genetics may be a determining factor in physical and athletic performance. But, could this also be true for African long-distance runners? Based on this question, this brief review proposed the role of genetic factors (mitochondrial deoxyribonucleic acid, the Y chromosome, and the angiotensin-converting enzyme and the alpha-actinin-3 genes) in the amazing athletic performance observed in African runners, especially the Kenyans and Ethiopians, despite their environmental constraints.

Bp-13 Pla2: Purification And Neuromuscular Activity Of A New Asp49 Toxin Isolated From Bothrops Pauloensis Snake Venom.

A new PLA2 (Bp-13) was purified from Bothrops pauloensis snake venom after a single chromatographic step of RP-HPLC on μ-Bondapak C-18. Amino acid analysis showed a high content of hydrophobic and basic amino acids and 14 half-cysteine residues. The N-terminal sequence showed a high degree of homology with basic Asp49 PLA2 myotoxins from other Bothrops venoms. Bp-13 showed allosteric enzymatic behavior and maximal activity at pH 8.1, 36°-45°C. Full Bp-13 PLA2 activity required Ca(2+); its PLA2 activity was inhibited by Mg(2+), Mn(2+), Sr(2+), and Cd(2+) in the presence and absence of 1 mM Ca(2+). In the mouse phrenic nerve-diaphragm (PND) preparation, the time for 50% paralysis was concentration-dependent (P < 0.05). Both the replacement of Ca(2+) by Sr(2+) and temperature lowering (24°C) inhibited the Bp-13 PLA2-induced twitch-tension blockade. Bp-13 PLA2 inhibited the contractile response to direct electrical stimulation in curarized mouse PND preparation corroborating its contracture effect. In biventer cervicis preparations, Bp-13 induced irreversible twitch-tension blockade and the KCl evoked contracture was partially, but significantly, inhibited (P > 0.05). The main effect of this new Asp49 PLA2 of Bothrops pauloensis venom is on muscle fiber sarcolemma, with avian preparation being less responsive than rodent preparation. The study enhances biochemical and pharmacological characterization of B. pauloensis venom.

Electrophysiologic Activity of the Vestibular Fold

Objectives: To assess the vestibular fold muscle after cordectomy and laryngeal reconstruction, the pattern of motor unit recruitment during sound emission, and the morphologic characteristics of motor unit action potentials. Design: Prospective analysis. Setting: Tertiary academic hospital. Patients: We evaluated 11 men (mean age, 65.7 years; age range, 53-82 years) who underwent laryngofissure, cordectomy, and laryngeal reconstruction with a vestibular fold flap. Interventions: Laryngeal electromyography with the insertion of a needle electrode for the assessment of the electrophysiologic activity of thyroartenoid muscle fibers and of the cricothyroid muscle on the operated on and nonoperated on sides. The thyroarytenoid muscle was evaluated by introducing a needle electrode through the thyroid cartilage and the cricothyroid membrane. Main Outcome Measures: Activities of needle insertion, spontaneous muscle activity during rest, and pattern of motor unit recruitment. Results: Seven patients (64%) had vestibular fold muscle fiber, all of whom showed motor unit recruitment in response to sound emission. No neurogenic muscle injuries were observed except in 1 patient with evidence of chronic injury. Conclusion: After cordectomy and laryngeal reconstruction, thyroarytenoid muscle fibers are present in the vestibular fold, with motor unit recruitment during sound emission.

Repeatability of maximal voluntary force and of surface EMG variables during voluntary isometric contraction of quadriceps muscles in healthy subjects

The repeatability of initial values and rate of change of EMG signal mean spectral frequency (MNF), average rectified values (ARV), muscle fiber conduction velocity (CV) and maximal voluntary contraction (MVC) was investigated in the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles of both legs of nine healthy male subjects during voluntary, isometric contractions sustained for 50 s at 50% MVC. The values of MVC were recorded for both legs three times on each day and for three subsequent days, while the EMG signals have been recorded twice a day for three subsequent days. The degree of repeatability was investigated using the Fisher test based upon the ANalysis Of VAriance (ANOVA), the Standard Error of the Mean (SEM) and the Intraclass Correlation Coefficient (ICC). Data collected showed a high level of repeatability of MVC measurement (normalized SEM from 1.1% to 6.4% of the mean). MNF and ARV initial values also showed a high level of repeatability (ICC > 70% for all muscles and legs except right VMO). At 50% MVC level no relevant pattern of fatigue was observed for the VMO and VL muscles, suggesting that other portions of the quadriceps might have contributed to the generated effort. These observations seem to suggest that in the investigation of muscles belonging to a multi-muscular group at submaximal level, the more selective electrically elicited contractions should be preferred to voluntary contractions. (C) 2001 Elsevier Science Ltd. All rights reserved.

Effect of the movement speed of resistance training exercises on sprint and strength performance in concurrently training elite junior sprinters

The aim of this study was to determine the effects of 7 weeks of high- and low-velocity resistance training on strength and sprint running performance in nine male elite junior sprint runners (age 19.0 +/- 1.4 years, best 100 m times 10.89 +/- 0.21 s; mean +/- s). The athletes continued their sprint training throughout the study, but their resistance training programme was replaced by one in which the movement velocities of hip extension and flexion, knee extension and flexion and squat exercises varied according to the loads lifted (i.e. 30-50% and 70-90% of 1-RM in the high- and low-velocity training groups, respectively). There were no between-group differences in hip flexion or extension torque produced at 1.05, 4.74 or 8.42 rad . s(-1), 20 m acceleration or 20 m 'flying' running times, or 1-RM squat lift strength either before or after training. This was despite significant improvements in 20 m acceleration time (P < 0.01), squat strength (P< 0.05), isokinetic hip flexion torque at 4.74 rad . s(-1) and hip extension torque at 1.05 and 4.74 rad . s(-1) for the athletes as a whole over the training period. Although velocity-specific strength adaptations have been shown to occur rapidly in untrained and non-concurrently training individuals, the present results suggest a lack of velocity-specific performance changes in elite concurrently training sprint runners performing a combination of traditional and semi-specific resistance training exercises.

Genetic disruption of the growth hormone receptor does not influence motoneuron survival in the developing mouse

In the rodent central nervous system (CNS) during the five days prior to birth, both growth hormone (GH) and its receptor (GHR) undergo transient increases in expression to levels considerably higher than those found postnatally. This increase in expression coincides with the period of neuronal programmed cell death (PCD) in the developing CNS. To evaluate the involvement of growth hormone in the process of PCD, we have quantified the number of motoneurons in the spinal cord and brain stem of wild type and littermate GHR-deficient mice at the beginning and end of the neuronal PCD period. We found no change in motoneuron survival in either the brachial or lumbar lateral motor columns of the spinal cord or in the trochlear, trigeminal, facial or hypoglossal nuclei in the brain stem. We also found no significant differences in spinal cord volume, muscle fiber diameter, or body weight of GHR-deficient fetal mice when compared to their littermate controls. Therefore, despite considerable in vitro evidence for GH action on neurons and glia, genetic disruption of GHR signalling has no effect on prenatal motoneuron number in the mouse, under normal physiological conditions. This may be a result of compensation by the signalling of other neurotrophic cytokines.

Coral snake venoms: mode of action and pathophysiology of experimental envenomation

Coral snakes, the New World Elapidae, are included in the genera Micniroides and Micrurus. The genus Mlcrurus comprises nearly all coral snake species and those which are responsible for human snake-bite accidents. The following generalizations concerning the effects induced by their venoms, and their venom-properties can be made. Coral snake venoms are neurotoxic, producing loss of muscle strenght and death by respiratory paralysis. Local edema and necrosis are not induced nor blood coagulation or hemorrhages. Proteolysis activity is absent or of very low grade. They display phospholipase A2 activity. Nephrotoxic effects are not evoked. The main toxins from elapid venoms are postsynaptic and presynaptic neurotoxins and cardiotoxins. Phospholipases A2 endowed with myonecrotic or cardiotoxin-like properties are important toxic components from some elapid venoms. The mode of action of Micrurus frontalis, M. lemniscatus, M. corallinus and M. fulvius venoms has been investigated in isolated muscle preparations and is here discussed. It is shown that while M. frontalis and M. lemniscatus venoms must contain only neurotoxins that act at the cholinergic end-plate receptor (postsynaptic neurotoxins), M. corallinus venom also inhibits evoked acetylcholine release by the motor nerve endings (presynaptic neurotoxin-like effect) and M. fulvius induces muscle fiber membrane depolarization (cardiotoxin-like effect). The effects produced by M. corallinus and M. fulvius venoms in vivo in dogs and M. frontalis venom in dogs and monkeys are also reported.