[Reloading of rat soleus after hindlimb unloading and serum insulin-like growth factor 1].

The aim of this study was to elucidate the effects of 14- day hindlimb suspension (HS) and subsqquent reloading (3 or 7 days) on the m. soleus mass, muscle fiber cross-sectional area (CSA), soleus fiber properties and serum IGF-1 in rats. Rats were hindlimb suspended for 14 days or kept as controls (C, n = 7). Soleus muscles were isolated after HS (HS, n = 7) or after reambulation for either three (R3, n = 5) or seven days (R7, n = 6). Frozen serial sections of m. soleus were stained by primary monoclonal antibodies against MHCI. For measurement of concentration IGF-1 in the blood serum, test-system for IFA DSL-10-2800 Non-Extraction IGF-1 ELISA was used. Muscle mass was significantly reduced in HS (-35 %) but subsequently increased with reloading in R3 (-10 % to C) and was recovered to control values in R7 (+5 % to C). Fiber CSA was significantly reduced (-43 %) in HS and was greater in R7 than in HS and slightly greater than in R3. 14 days of HS resulted in a mean maximal tension reduced by 35 %. After 7 days of subsequent reloading the mean maximal specific tension was still low (-33 % to C) and didn't differ from HS level. The level in blood IGF-1 has obviously decreased during 14-day unloading by 48 %, remained at the same level in R3, and increased 10 fold in R7.

Influence of hindlimb suspension on calcium-induced contraction characteristics in dystrophin-deficient animals.

The direct data concerning effects of unloading on dystrophic muscle were received in study of mdx mice, a model for Duchenne muscular dystrophy, muscles before and after hindlimb suspension. Experiments were performed on softer skinned soleus muscle fibers isolated from wild-type (C57black) as a control and mdx mice aged 2 weeks. Animals of two experimental groups were tail suspended during 21 days. In both groups of hindlimb suspended mice isolated soleus fibers were thinner than in the control groups. But there was a greater 37% significant decrease in fiber diameter in wild-type (CHS) suspended mice vs. 24% in mdx (MHS) suspended group. Values of absolute peak tension in CHS were less than in the control group by 33%, and in MHS mice suspended--by 39%. 21 days of hindlimb suspension resulted in reduction of mean peak specific tension by 28% in MHS and significantly less drop (15%) in CHS groups. We observed a similar rightward shift of the tension pCa curve in both mice strains.

[Creatine as a metabolic controller of skeletal muscles structure and function in strength exercises in humans. The cellular mechanisms].

The effects of creatine oral supplementation combined with a 10-week resistive training of morphometric, contractile and molecular characteristics of human vast lateral muscle fibers were studied. 2 groups consisting of 9 young healthy men each were involved in resistive training of knee extensors for 10 weeks. Volunteers of the first group received per os 20 g of creatine for the 1st week of training and 5 g for the rest of the experimental training period. We found a significant increase of slow and fast-twitch fiber size in both trained groups and a significant increase of Ca-sensitivity of skinned single fiber contractility in creatine-supplemented group. The serum creatine phosphokinase activity in blood samples taken 24 hours after exercise session increased in all stages of the experimental training in both groups. At the same time, the adaptive decrease of the after-exercise CK concentration was observed in the placebo but not in the creatine-supplemented group. The altered integrity of the subsarcolemmal dystrophin layer was revealed in both groups after training.

[Human soleus fibers contractile characteristics and sarcomeric cytoskeletal proteins after gravitational unloading. Contribution of support stimulus]. / Sokratitel'nye kharakteristiki i belki sarkomernogo tsitoskeleta volokon m. soleus cheloveka v usloviiakh gravitatsionnoi razgruzki. Rol' opornogo stimula.

The effects of support withdrawal and support stimulation on the contractile characteristics of human soleus fibers and cellular factors which influence them were studied. The experimental model of the "dry" head-out water immersion was used in the study. In this model, the hydrostatic pressure on different sites of the body surface are equal so that the experimental conditions are close to the complete supportlessness. A 7-day exposure to dry immersion resulted in a decrease in the maximal isometric tension of the skinned fibers, a decline in the myofibrillar Ca2+-sensitivity, and the relative loss of the titin and nebulin content. A significant decrease in the percentage of fibers containing slow myosin heavy chains was also observed after dry immersion. The application of the mechanical stimulator influencing the plantar support zones with a pressure of 0.2 +/- 0.15 kg/cm2 6 times a day for 20 minutes of each hour brought about a complete prevention of the above listed effects of dry immersion. The data obtained allow one to conclude that the decline in maximal tension and Ca2+-sensitivity as well as myosin shift and loss of sarcomeric cytoskeletal proteins are associated with the support withdrawal during the exposure to dry immersion.

Afferent and peripheral control of muscle fiber properties during gravitational unloading.

The present paper covers two series of the experiment studies performed in attempt to analyze the support-triggered cellular mechanisms, controlling the maintenance of tonic muscle fiber characteristics. Exposure to 7 day dry immersion induced significant decline of the human soleus single fiber peak isometric tension and the Ca(2+)-sensitivity of myofibrils. 30-40% losses of the relative content of titin and nebulin were found after immersion. The application of the plantar support stimulation device prevented all these alterations. In the second experimental series the treatment of hindlimb suspended rats with the Ca(2+)-binding agent (EGTA) allowed to prevent or attenuate all the above mentioned unloading-induced soleus fiber alterations. Thus it is concluded that resting Ca2+ accumulation in the unloaded fibers may be among the mechanisms involved in the changes of fiber properties during unloading.

Effects of artificial support stimulation on fiber and molecular characteristics of soleus muscle in men exposed to 7-day dry immersion.

Artificial support stimulation is known to attenuate or prevent many motor or skeletal muscle effects of actual or simulated microgravity. The present study was purposed to analyze the effects of artificial support on human soleus fibers after 7-day exposure to supportless environment. 8 healthy male volunteers were exposed to dry immersion in supine position for 7 days according to Shulzhenko and Vil-Villiams (1972). 4 of them worn the support device which provided them with plantar stimulation in regime described elsewhere.

[Contractile characteristics of single skinned rat soleus muscle fibers under gravitational load: effects of a calcium-binding agent]. / Sokratitel'nye kharakteristiki odinochnykh skinirovannykh volokon Musculus soleus krysy v usloviiakh gravitatsionnoi razgruzki: éffekty kal'tsiisviazyvaiushchego agenta.

Excessive intracellular calcium accumulation is believed to trigger the development of functional and structural changes in muscle fibers under microgravity conditions. The hypothesis was testified in the 14-day hindlimb suspension study with the application of a Ca(2+)-binding agent (10% EGTA). Twenty one rats were divided into 3 groups: cage controls (7), hindlimb-suspended rats that received intraperitoneal injections of saline (7), and hindlimb-suspended rats with EGTA treatment. Whereas the diameter of muscle fibers of unloaded rat soleus muscle was 20% less than in the control group (and there were no significant differences between rats with injections of EGTA and without them), the decrease of maximal tension was more pronounced (more than 50%). This discrepancy resulted in a decrease of maximal specific tension. The value of absolute tension in rats treated with placebo was by 52%, and in EGTA-treated rats by 41% less than in the control group. Thus, there were no significant differences in specific tension between this group and the control group. Obviously, the injections of EGTA prevented the effects of those mechanisms that induce a decline of tension in muscle fibers but are not linked with the reduction of fiber size. The Ca/tension curve in hindlimb-suspended saline-treated rats shifted to the right so that the pCa thresholds changed from 6.85 +/- 0.03 in cage controls to 6.70 +/- 0.04 (p < 0.05), which indicates that myofibrils of unloaded soleus are less sensitive to Ca2+. At the same time, the pCa threshold in EGTA-treated hindlimb-suspended rats was 6.93 +/- 0.02. It is concluded that chronic binding of excess calcium results in an increase in Ca sensitivity indices.