High proportion of type I fibres in thigh muscle of young dancers

A previous study showed that adult female dancers have a high percentage of type I fibres in vastus lateralis. similar to that of endurance-trained female runners ar female cross-country skiers. It is not known if dancers already at an early age are characterized by a high percentage of type I fibres or develop a high percentage of type I fibres as a consequence of dance training. Furthermore. the muscle fibre composition of male dancers has not previously been studied. Therefore the aim of the study was to analyse skeletal muscle fibre characteristics in 10-year-old and 20-year-old dancers of both sexes. Age-matched boys and girls whose physical activity was average for their age groups served as controls. Muscle biopsies for histochemical analysis were obtained from vastus lateralis using the percutaneous needle technique. The major finding of the present study was that the vastus lateralis of young dancers of both sexes had a higher percentage of type I fibres than that of controls. Moreover. the higher type I percentage was seen not only in 20 year aids. but also in 10 year aids. who had begun their dance training at a professional level only a few weeks earlier. No significant difference in this respect was found between female and male dancers. In conclusion. the muscle fibre type composition in young dancers of both sexes differs from that of the average individual of the same age and is characterized by a high percentage of type I fibres.     

Simultaneous measurement of intracellular pH and contraction in uterine smooth muscle

Changes in intracellular pH (pH_i) are thought to produce large changes in force production in the uterus. There have however, been no simultaneous measurements of pH_i and force in the uterus and therefore no direct information is available about the relation between the two. We have used carboxy-SNARF (a pH-sensitive fluorophore) in small strips of longitudinal myometrium and obtained simultaneous measurements of pH_i and force. SNARF did not alter contractile function, and continuous measurements of pH_i could be made for 2 hours. The mean resting pH_i (7.16) was similar to that reported previously. Application of weak bases rapidly raised pH_i, in a concentration-dependent manner, followed by a gradual restoration of pH_i to resting levels. Alkalinization greatly increased the frequency of contractions, often accompanied by a small increase in their amplitude. Removal of base produced a rebound acidification which transiently abolished contractions. Direct acidification of the cytoplasm, by application of weak acid, also abolished contractions. However the alkalinization which accompanied removal of acid, produced variable effects on force.Supported by the M.R.C.     

汞对人体必需元素干扰的研究

对42例汞吸收、2例汞中毒者(尿汞>99.7nmol/L),采用原子吸收光谱法,检测了汞对人体必需五种金属元素代谢的干扰。研究发现,汞时人体必需元素镁、铜具有拮抗作用。汞吸收者血清镁极显著低于对照组(P>0.01)。经驱汞治疗后,血清镁、铜自然上升与对照组无统计学差异(P>0.05),镁离子低下,可出现神经肌纤维兴奋性增高。由此推测,汞引起肌肉震颤的毒理,可能由汞拮抗镁离子低下引起。设想,对汞中毒者采用补镁制剂治疗,是否具有驱汞作用值得探讨。     

Effects of phorbol ester on carbachol-induced contraction in bovine ciliary muscle: possible involvement of protein kinase C

The aim of the research was to characterize muscarinic receptors of bovine ciliary muscle and to investigate the desensitization process. The role of protein kinase C was analyzed. The results show that muscarinic receptors of bovine ciliary muscle have the pharmacological characteristics of the M₃ subtype. Acute exposure to phorbol esters (1 μM phorbol 12,13-dibutyrate, PDB, or 0.1 μM phorbol 12-myristate 13-acetate, PMA, for 15 and 5 min, respectively) resulted in antagonism of muscarinic receptor-mediated contraction. Long-term pretreatment (18 h) with PMA to down-regulate protein kinase C resulted in potentiation of carbachol-induced contraction, reduction of agonist-induced desensitization and loss of phorbol ester-induced desensitization. Staurosporine (3 μM) and H₇ [1-(5-isoquinolinesulfonyl)-2-methyl-piperazine] (1 μM), protein kinase C inhibitors, produced a significant potentiation of the contractile effect of carbachol, reduced the desensitization produced by repeated addition of carbachol and suppressed that induced by phorbol esters. In vitro incubation with carbachol, PDB or PMA did not cause any modification of the binding of labeled [³H]quinuclidinyl benzilate. In vitro incubation with PDB and PMA produced, as expected, a significant translocation of protein kinase C from the cytosol to the membrane. The incubation of the ciliary muscle with carbachol, using the protocol of exposure that induced maximal desensitization of contractile responses, produced a significant redistribution of the enzyme from the cytosol to the membrane. These findings suggest that agonist-induced modulation of functional cholinergic sensitivity in ciliary muscle is correlated, at least partially, to the translocation of protein kinase C from the cytosol to the membrane. The desensitization by phorbol esters is completely due to protein kinase C activation; during the desensitization process, direct modification of the density and affinity of muscarinic receptors is not involved.     

The effect of ionic strength on the kinetics of rigor development in skinned fast-twitch skeletal muscle fibres

 Recent atomic 3-D reconstructions of the acto-myosin interface suggest that electrostatic interactions are important in the initial phase of cross-bridge formation. Earlier biochemical studies had also given strong evidence for the ionic strength dependence of this step in the cross-bridge cycle. We have probed these interactions by altering the ionic strength (Γ/2) of the medium mainly with K⁺, imidazole⁺ and EGTA^2– to vary charge shielding. We examined the effect of ionic strength on the kinetics of rigor development at low Ca²⁺ (experimental temperature 18–22°C) in chemically skinned single fast-twitch fibres of mouse extensor digitorum longus (EDL) muscle. On average the delay before rigor onset was 10 times longer, the maximum rate of rigor tension development was 10 times slower, the steady-state rigor tension was 3 times lower and the in-phase stiffness was 2 times lower at high (230 mM) compared to low (60 mM) ionic strength. These results were modelled by calculating ATP depletion in the fibre due to diffusional loss of ATP and acto-myosin Mg.ATPase activity. The difference in delay before rigor onset at low and high ionic strength could be explained in our model by assuming a 15 times higher Mg.ATPase activity and a threefold increase in K _m in relaxing conditions at low ionic strength. Activation by Ca²⁺ induced at different time points before and during onset of rigor confirmed the calculated time course of ATP depletion. We have also investigated ionic strength effects on rigor development with the activated troponin/tropomyosin complex. ATP withdrawl at maximum activation by Ca²⁺ induced force transients which led into a ”high rigor” state. The peak forces of these force transients were very similar at low and high ionic strength. The subsequent decrease in tension was only 10% slower and steady-state ”high rigor” tension was reduced by only 27% at high compared to low ionic strength. Addition of 10 mM phosphate to lower cross-bridge attachment strongly suppressed the transient increases in force at high ionic strength and reduced the steady-state rigor tension by 17%. A qualitatively similar but smaller effect of phosphate was observed at low ionic strength where steady-state rigor force was reduced by 10%. The data presented in this study show a very strong effect of ionic strength on rigor development in relaxed fibres whereas the ionic strength dependence of rigor development after thin filament activation was much less. The data confirm the importance of electrostatic interactions in cross-bridge attachment and cross-bridge-attachment-induced activation of thin filaments. Received: 3 September 1997 / Received after revision and accepted: 12 December 1997     

Plastic surgical treatment of a chronic thoracic duct fistula using a sternocleidomastoid muscle flap — a case report

Thoracic duct fistula is a rare but potentially serious complication of head and neck surgery. Such fistulae may be difficult to treat, and several techniques, both operative and non-operative, have been advocated. A case of successful surgical treatment of a chronic thoracic duct fistula is presented. The fistula occurred in a 51-year-old female following treatment of a solitary supraclavicular breast metastasis by local excision and radiotherapy. The divided duct was ligated and the area was covered with the clavicular head of the sternocleidomastoid muscle.     

Can a Single Muscle Fiber Model the Features of Myocardial Stunning?

The exact mechanisms that cause myocardial stunning are still unclear. We previously utilized a computer model of the ventricle that was effective in modeling the dominant observable features of stunning, but it was not simple to implement. This led to the design of a single muscle fiber model. The mathematical model of a muscle fiber consisted of three elements: a contractile element, a series elastic element, and a parallel elastic element. The model created length waveforms based on time-dependent force and contractile stiffness functions. This model was initially evaluated by entering the same regional parameter values used in the global dual region ventricular model. First a reduction of the contractile stiffness function was applied by reducing the peak stiffness by 30%, and then the rates of activation and deactivation were reduced by 20% while maintaining the peak values constant. The three-element model produced results very similar to the canine and ventricular model. Thus, it is concluded that the simpler three-element model provides an accurate model of the myocardial tissue and its deficiencies during stunning.     

Chest Wall Implants: Their Use for Pectus Excavatum,Pectoralis Muscle Tears,Poland's Syndrome,and Muscular Insufficiency

Solid customized and prefabricated silicone implants have been used by the author for 15 years in a wide range of chest wall deformities. Chest wall implants are often used in males seeking to augment a muscularly deficient or underdeveloped chest; however, their greatest use has come in a variety of deformities both congenital and acquired, such as pectus excavatum, Poland's Syndrome, and pectoralis muscle tears. The implants can be either customized using a moulage technique or are prefabricated, manufactured implants which can be modified on the operating table to repair the contour deformity. The immediate postoperative problem of seroma and subcutaneous implant ``show' has been minimized by careful planning, gentle technique, deep insertion, improved patient positioning on the operating room table, and the use of oral anti-inflammatory medications. The long-term results of these implants seem very satisfactory. The patients are usualy physically active, and the implants show no long-term sequelae such as seroma, infection, displacement, or rupture.     

理气类中药对大鼠离体胃平滑肌条的作用

目的：观察理气类中药对大鼠离体胃平滑肌条运动的影响。方法：将肌条放置在灌流肌槽中，用生理记录仪记录肌条的收缩活动。结果：陈皮、枳实对胃各部位平滑肌条均为抑制效应，香附、薤白、木香、柿蒂、乌药对胃底肌条为兴奋效应，但对其他部位肌条则表现为兴奋或抑制不同的效应，沉香仅降低胃窦环行肌收缩波平均振幅，对其他肌条无影响。结论：理气类中药对大鼠离体胃平滑肌条既有兴奋作用，也有抑制作用。