Native skeletal muscle dihydropyridine receptor exists as a supramolecular triad complexRID="†"ID="†" Research Article

One of the central elements of excitation-contraction coupling, the voltage-sensing dihydropyridine receptor, is believed to exist as a high-molecular-mass complex in the triad junction. Although freeze-fracture electron microscopical analysis suggests a tetrad complex, no direct biochemical evidence exists demonstrating the actual size of the native membrane complex. Using a combination of various two-dimensional gel electrophoresis techniques, we show here that the principal α ₁-subunit of the dihydropyridine receptor and its auxiliary α ₂-subunit form a triad complex of approximately 2800 kDa under native conditions. Established Ca²⁺-ATPase tetramers and calsequestrin monomers were employed for the internal standardization of the gel systems used. Thus, the large voltage-sensing complex appears to be tightly associated, since it does not disintegrate during subcellular fractionation and native electrophoresis procedures. Our findings support the cell biological hypothesis that native dihydropyridine receptor units form a tetrad structure within the transverse tubules. Received 10 October 2000; revised 28 November 2000; accepted 4 January 2001     

Is glycogen a major energy source in avian gizzard smooth muscle contraction?

Summary In comparison to other avian smooth and striated muscles, chicken gizzard contains very low levels of glycogen. This myoglobin-rich muscle seems to derive the energy for its powerful contraction from other sources.Support by the Deutsche Forschungsgemeinschaft (Ste 105/25-2) is gratefully acknowledged.     

In vitro stability and protein composition of thick filaments from insect flight muscles

Thick and thin filaments of synchronous and asynchronous insect flight muscles were separated by density gradient centrifugation. A good release of myofilaments from myofibrils was obtained by sonication of myofibrils in relaxing solution with pH 6.1 (locust), pH 6.4 (honeybee) and pH 6.6 (fleshfly), respectively. Thick filaments but not thin filaments were dissolved, if sucrose gradient centrifugation was used to separate the filaments. Thus, sucrose gradients are the medium of choice if actin filaments are to be purified. Glycerol-containing gradients selectively dissolved myosin filaments from fleshfly muscles. The stability of the myosin filaments of all muscles was sufficient in gradients with 10–30% formamide.     

Serum creatine kinase in marathon runners

Summary Serum creatine phosphokinase (CK) and CK-MB activity were determined in 21 trained runners participating in a marathon race (42.2 km). Enzyme activities immediately after the race increased two to three times compared with activities before the race. The greatest increases were found in the slowest runners, suggesting greater skeletal muscular trauma in the least trained or fit. As these are likely to include the older athletes who are also more likely to suffer acute myocardial injury during strenuous exercise, our findings assume special import in the interpretation of increased CK and CK-MB serum activities of older athletes.Acknowledgments. The authors wish to thank the members and president of the Columbia Track Club for their cooperation.     

Effect of phosphorylation of myosin light chains on interaction of heavy meromyosin with regulated F-actin in ghost fibers

Summary The binding of phosphorylated heavy meromyosin to regulated F-actin in ghost fibers at high Ca²⁺ concentration increases, and at low Ca²⁺ concentration decreases, the anisotropy of intrinsic tryptophan fluorescence of F-actin. The effect is opposite to the effect of the binding of dephosphorylated heavy meromyosin.     

肌氧含量的光电无损检测及其在运动训练中的应用

介绍了动脉血氧和肌氧饱和度的概念。从光与组织之间相互作用的内在机理出发，给出了无损光电监测组织中氧含量的基本原理和方法，并推导了计算公式。对运动员在训练过程中肌肉氧代谢能力进行了实时连续无损检测和评估，随着运动状态的改变，明显看到了肌氧含量的变化。测试结果表明，运动员在运动训练过程中及训练后恢复期的氧消耗和恢复与运动强度明显相关。这对于进一步评定训练效果，掌握训练强度，判断疲劳以及运动员选材的深入研究提供了重要的参考价值。     

3-甲基组氨酸三室模型在研究猪骨骼肌蛋白质降解中的应用

3-甲基组氨酸(3MH)主要是动物骨胳肌蛋白分解代谢产物，它不能再用于合成蛋白，因而3MH是研究动物骨胳肌蛋白降解率的一个可行示踪物．将标记的3MH经颈静脉注射，对血液中的同位素丰度进行观测，再根据猪体内3MH代谢特点，构建出猪骨胳肌蛋白降解的三分域模型．本文着重对该模型的的理论基础进行了讨论。     

Alanine and aspartate aminotransferases in normal and denervated skeletal muscle

Summary Activities of alanine and aspartate aminotransferases are maintained during the first 5 weeks of growth, but decrease subsequently in normal chick gastrocnemii. In sciatectomized muscles, a 5-fold elevation in these enzymes reveals increased utilization of amino acid as a compensatory metabolic support during denervation atrophy.     

Muscle proteinase activities during compensatory growth and atrophy

Summary Specific activities of cathepsins B and D, but not H, increased in both the tenotomized gastrocnemius and functionally overloaded soleus muscles, thus correlating with previously reported increases in protein degradation. Subsequent denervation of the overloaded soleus caused an additive increase in proteolysis, suggesting a possible greater lability of proteins in this muscle.     

Embryonic chick muscle produces an FGF-like activity

Normal and pathological formation of blood vessels is of considerable interest both in terms of basic scientific processes and clinical applications. Angiogenic events in the adult are likely to represent persistence of developmental mechanisms, and embryos are therefore a suitable experimental model for these processes. Among embryonic tissues, muscle is particularly appropriate for investigation, since it is highly vascularised from early stages. There are a number of competing explanations of how this process is controlled. Bioassays offer advantages over conventional molecular localisation techniques, in that they reveal the presence of active processed forms of the molecules under study, rather than non-processed forms, or non-translated meassages. Using these techniques, we report here that embryonic chick muscle, taken from the stages at which blood vessels are forming, produces an angiogenic activity on the chick chorioallantoic membrane (CAM), and transforms NR6 cells in soft agar. Basic fibroblast growth factor (bFGF) is shown to be angiogenic on the CAM in the same way, and also transforms NR6 cells (NR6 cells lack functional epidermal growth factor/transforming growth factor-a receptors, and are believed to respond only to bFGF in this way). Anti-bFGF removes the transforming activity of the embryonic muscle. We conclude that this represents evidence that embryonic chick muscle is producing an FGF-like molecule which is capable of acting as an angiogenic agent at the appropriate times in development.