Selectivity of alterations in skeletal fibers in chronic Chagas' disease of the mouse

Summary In mice chronically infected withTrypanosoma cruzi, the masseter muscle (rich in type II fibers) was devoid of inflammatory infiltrates and parasites. In contrast, other muscles, composed of type I and II fibers, showed a decrease of type I fibers, parasites and lesions, suggesting that inT. cruzi infection type I muscle fibers are selectively damaged.     

Satellite cells in the regenerated and regrafted skeletal muscles of rats

Summary Soleus (SOL) muscles were grafted into extensor digitorum longus (EDL) muscle beds (EDL-first-graft). Sixty days later, some mature EDL-first-grafts were regrafted into their own beds (EDL-second-grafts). Fully regenerated muscle fibers and satellite cells were observed in both types of mature grafts. The ratios of satellite cell nuclei per total nuclei (myonuclei and satellite cell nuclei) were 4.81±0.47% for EDL-2nd graft, 4.26±0.51% for EDL-1st-graft, 4.30±0.33% for control SOL, and 3.30±0.18% for control EDL. It is thought that satellite cells are required for the repeated activity of muscle fiber regeneration. The persistance of satellite cells in EDL-second-grafts suggests that satellite cells are not depleted during the first grafting, making second-grafts possible.     

New views of smooth muscle structure using freezing,deep-etching and rotary shadowing

Summary Freezing, deep-etching and rotary shadowing techniques have been applied to study smooth muscle ultrastructure. The results show some new aspects of intracellular and extracellular connections, interior views of the sarcoplasmic reticulum showing a luminal content, coated pits and vesicles, contractile filaments and other organelles in smooth muscle.     

The effect of exercise on protein turnover in isolated soleus and extensor digitorium longus muscles

Summary The rate of protein degradation was found to be increased in isolated soleus and extensor digitorum muscles of 60–80 g rats after exercise consisting of running for 120 min. These findings support the hypothesis that exercise causes an increase in skeletal muscle protein degradation, and that both red and white muscles are affected similarly.     

Effect of L-carnitine and stimulated lipolysis on muscle substrates in the exercising rat

Summary To test the effect of L-carnitine on glycogen sparing when fat oxidation is increased, 100 mg/kg/d were given to rats orally for 3 days, resulting in 1.8-fold higher muscle carnitine levels. Even when FFA were raised by heparin-stimulated lipolysis, the rate of glycogen degradation was not reduced during exercise.     

Involvement of thiols in the induction of inward current induced by silver in frog skeletal muscle membrane

Exposure of voltage-clamped frog skeletal muscle fibres to silver caused a maintained inward current which could be carried by Ca²⁺, Mg²⁺ or Na⁺. Inorganic Ca²⁺ channel blockers and dithiothreitol (SH reducing agent) diminished this current, but a Na⁺ channel blocker did not. Thus, silver activates the Ca²⁺ channel by acting on SH groups in a Ca²⁺ channel protein.     

Selective killing of smooth muscle cells in culture by the ricin A-chain conjugated with monoclonal antibodies to a cell surface antigen via a dextran bridge

Summary Monoclonal antibodies to a surface antigen of the modulated smooth muscle cells originally isolated from the rat aorta media were conjugated with ricin A-chain via an oxidized dextran bridge. The interaction of cultured cells with the conjugates obtained and with control substances was monitored following incorporation of¹⁴C-leucine radioactivity. It was found that¹⁴C-leucine incorporation was suppressed by 80–90% at a conjugate concentration of 10^–6–10^–7 M. Antigen-negative cells (line IAR; rat hepatocytes) were insensitive to the conjugate at any concentration used. Control use of purified ricin A-chain, native or oxidized dextran, specific and nonspecific IgG did not affect normal¹⁴C-leucine incorporation. The data obtained may be useful for designing targeted drug transport systems and for selective screening of modulated smooth cells in vascular pathology models in vivo.     

Structural characteristics and distribution of satellite cells along crayfish muscle fibers

The distribution of satellite cells (sc) in long-sarcomere muscle fibers from the carpopod extensor muscle of the crayfish (Astacus fluviatilis) has been studied electron-microscopically. The sc are spindle-shaped and are oriented parallel to the long axis of a fiber. The mean lengths of sc nuclei (17.00 m) and that of myonuclei (18.35 m) differ non-significantly. In older animals, the mean ratio of the number of sc nuclei to the total number of nuclei (sc nuclei + myonrclei) is 0.0716, 0.0848, and 0.034 for the tendon, central and shell segments, respectively. The corresponding values for younger animals are 0.158, 0.166, and 0.081. The mean numbers of sc nuclei per mm of a fiber are 94, 117, and 47 (older animals), and 164, 117, and 94 (younger animals) for the tendon, central and shell segments, respectively. The high incidence of sc per unit fiber length in crayfish may be related to the fact that crayfish muscle fibers have a much larger diameter than vertebrate muscle cells.     

The physiology of the smooth muscle: an interdisciplinary review—part II

Summary In the guinea pig taenia coli, when glycogen is depleted by repeating Ca-induced contracture in excess K solution containing no glucose, the tension cannot be maintained. The decrease in tension is accompanied by reduction of high energy phosphate compounds and oxygen consumption. When substrate is readmitted to the glycogendepleted preparation in the presence of 2.4 mM Ca and 20 mM K, the first response is hyperpolarization of the membrane and relaxation, and this is followed by depolarization and development of contracture. The latter response is blocked by verapamil, suggesting that energy supply increases the Ca conductance of the plasma membrane. The early response is considered to be due to activation of electrogenic Ca pump, since this is not affected by ouabain as well as removal of Na and K. ATP produced by substrate readmission is probably preferentially utilized for Ca pump activation to reduce the intracellular. Ca. The recovery of tension is likely to be brought about by ATP supply not only to the contractile machinery but also to the plasma membrane to remove inactivation of Ca conductance. It is postulated that as the energy source is depleted, energy consumption is automatically limited by suppressing Ca influx, as a selfdefence mechanism. Since HB is as effective as glucose in the recovery of these processes, and also in the activation of electrogenic Na pump, the matabolic pathway of oxidative phosphorylation alone can support these functions without a contribution of the glycolytic pathway.     

Bionic jumping dynamics of the musculoskeletal leg mechanism for quadruped robots

As the pneumatic artificial muscle(PAM) has flexibility properties similar to biological muscle which is widely used in robotics as one kind of actuators,the bionic mechanism driven by PAMs becomes a hot spot in robotics.In this paper,a kind of musculoskeletal leg mechanism driven by PAMs is presented,which has three joints driven by four PAMs.The jumping movement is divided into three phases.The forward and inverse kinematics of the leg mechanism in different jumping phases is derived.Considering the ground reaction force between feet and environment,the dynamic in different jumping phases is analyzed by Lagrange method,then the relationship between PAM driving force and the joints angular displacement,angular velocity,angular acceleration during one jumping cycle is obtained,which will lay a foundation for the jumping experiment of the musculoskeletal leg mechanism.