Effect of weightlessness on the ultrastructure of rat striated muscles

The ultrastructure of rat striated muscles fixed on the 13th day of space flight was studied. It was found that adaptive atrophic and degenerative changes occur in parallel with atypical cellular and intracellular regeneration. The muscles are not completely restored after a 14-day readaptation on the Earth. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 124, No. 11, pp. 586–590, November, 1997     

Congenital hypothalamic hamartoma syndrome: Nosological discussion and minimum diagnostic criteria of a possibly familial form

We report on congenital hypothalamic hamartomas, discovered at autopsy in 3 unrelated fetuses. In the first 2 patients, the tumor was associated with skeletal dysplasia only. In the third patient, it was part of a non-random congenital malformation association, suggestive of Meckel syndrome. In one family, a previous boy died soon after birth with similar craniofacial and skeletal abnormalities. As far as we know, the association between isolated skeletal dysplasia and congenital hypothalamic hamartomas has not yet been documented in the literature. Nevertheless, a spectrum of skeletal abnormalities has been described in association with congenital hypothalamic “hamartoblastoma” and a constellation of variable visceral malformations under the eponym of “Pallister-Hall syndrome” (PHS). A detailed analysis of the PHS reported cases shows that only skeletal dysplasia and oro-facial abnormalities are present constantly. They show similarities with those found in our first 2 cases. These findings prompt us to consider skeletal dysplasia and oro-facial abnormalities as common denominator and minimum criteria required to define a nosologically distinct, possibly familial entity, which we suggest calling “congenital hypothalamic hamartoma syndrome” (CHHS).     

The ancestry of spondyloepimetaphyseal dysplasia with joint laxity (SEMDJL) in South Africa

Comprehensive genealogical investigations have been undertaken in eight families in the Afrikaans-speaking community of South Africa, in which at least one person had spondyloepimetaphyseal dysplasia with joint laxity (SEMDJL). All eight families had ancestral links with two females. These women had multiple marriages and cohabitations during the late 17th and early 18th centuries and they were 12 generations removed from the affected individuals. The identification of these common progenitors confirmed the syndromic homogeneity of SEMDJL in South Africa and permitted recognition of numerous obligate heterozygotes, thus facilitating biomolecular investigations of the basic defect.     

Satellite cells express the trophic factor IGF-I in regenerating skeletal muscle

The expression of insulin-like growth factor I (IGF-I, somatomedin C) was studied in regenerating skeletal muscle. Irreversible damage to skeletal muscle cells was induced in the extensor digitorum longus muscle (EDL) of adult rats by ischaemia, preceded by glycogen depletion, and the regeneration process was studied for periods up to 14 days after injury. The IGF-I was demonstrated by indirect immunofluorescence. Immunoreactivity against ribonucleotide reductase (RR) was used as a marker for DNA synthesis, that is, cell proliferation. Increased IGF-I immunoreactivity could be demonstrated within 24h after injury in satellite cells, intramuscular nerves and in blood vessels. The IGF-I immunoreactivity remained virtually unchanged in the contralateral, undamaged EDL. An increasing number of satellite cells, expressing high IGF-I immunoreactivity, could be demonstrated in the injured EDL, and within 72 h myoblasts, expressing high IGF-I and RR immunoreactivity, were formed. Small immature muscle cells, displaying high IGF-I immunoreactivity, were observed 4 days after injury. Increased IGF-I immunoreactivity was still obvious in the regenerated muscle cells 14 days after injury while RR immunoreactivity was seen only in scattered satellite cells. It is concluded that IGF-I may act as a trophic factor during regeneration of skeletal muscle after injury.     

Expression pattern of Popdc2 during mouse embryogenesis and in the adult.

The Popdc2 gene is a member of the Popeye domain containing gene family encoding membrane proteins with prominent expression in striated and smooth muscle tissue. After introducing a LacZ reporter gene into the Popdc2 locus, expression was studied during embryonic development and postnatal life. At embryonic day (E) 7.5, expression was present in cardiac and extraembryonic mesoderm. At E10.5, expression was found in heart, somites, and mesothelial cells lining the coelom. At E12.5, expression was present in the coelomic mesothelium, pericardial and myocardial layer of the heart, skeletal muscle, bladder, gut, and umbilical vessels. Postnatal expression was found in cardiac and skeletal muscle and in the smooth muscle layer of colon, rectum, and bladder. In the stomach, Popdc2 was exclusively present in the pyloric epithelium. In conclusion, Popdc2 is expressed in various muscle and nonmuscle cell types during embryonic development and in postnatal life.     

血管内皮生长因子受体在鼠横纹肌的表达与羟基磷灰石/碳纳米管复合材料毒性研究

目的 从观察鼠骨骼肌组织形态学改变和VEGF表达的角度研究CNTs/HAP纳微米复合材料对鼠骨骼肌的细胞毒性。方法 将CNTs/HAP纳米复合材料植入实验鼠臀大肌。按不同时间取材，做组织学观察和RT-PCR分析。结果 1d、3d显微镜下观察，炎细胞和淋巴细胞浸润伴轻度水肿、间质疏松；5d、7d显微镜下观察血管壁增厚，单核巨噬细胞和纤维组织增生，少量肌纤维出现变性，VEGF表达呈上升趋势；14天显微镜下观察周围组织间质血管扩张，仅有少量炎细胞浸润，水肿不明显，VEGF表达呈下降趋势。结论 CNTs/HAP对鼠骨骼肌细胞无毒性，有利于血管的再生，具有良好的生物相容性。     

The human force:velocity relationship; activity in the knee flexor and extensor muscles before and after eccentric practice

The human voluntary force:velocity relationship frequently fails to demonstrate the expected high eccentric forces. Possible explanations include unique activation strategies which might be affected by neural learning mechanisms. We investigated the effect of practicing eccentric contractions on (1) the force: velocity relationship of the human knee extensor muscles and (2) the extent of agonist and antagonist muscle activity. Eight healthy adults [seven women, group mean age 31 (SEM 5) years ± ] practised twice a week for 4 weeks using their non-dominant legs. Each session comprised three isokinetic concentric and eccentric maximal voluntary contractions (MVC) at randomised angular velocities of 100, 200 and 300° · s⁻¹. Before and after, the force:velocity relationship was determined bilaterally (angular velocities 0–300° · s⁻¹). There were no significant differences in the forces generated or relative electromyogram (EMG) activity after practice, although there was a trend for dynamic forces to increase. Beforehand, the bilateral eccentric MVC forces were lower than isometric (P < 0.0025); afterwards they were broadly similar. The agonist EMG was similar during isometric and eccentric contractions, but lower during concentric (P < 0.03). Antagonist EMG activity showed considerable individual variation, was similar during all contraction types and tended to be greater during dynamic contractions. These data indicate that neither central learning mechanisms nor total muscle activation strategies underlie the human failure to produce the expected high eccentric voluntary forces in humans. Accepted: 19 September 2000     

Increase in the proportion of fast-twitch muscle fibres by sprint training in males

Fifteen male physical education students were studied. The subjects trained for 4–6 weeks, 2–3 days per week, on a mechanically braked bicycle ergometer. A training session consisted of repeated 30-s ‘all-out’ sprints on a Wingate bicycle ergometer, on which the brake band of the flywheel was loaded with 75 g kg^-1 body wt, with rest periods of 15–20 min between consecutive sprints. Thigh muscle biopsies were taken before and after the training period and were analysed for fibre types using a myofibrillar ATPase stain. The proportion of type I fibres decreased from 57 to 48% (P < 0.05) and type IIA fibres increased from 32 to 38% (P < 0.05). This study indicates that it is possible to achieve a fibre type transformation with high-intensity training. The effect of two-legged ‘sprint’ training on muscle fibre type composition may be related to a changed pattern of muscle fibre activation (e.g. an increased stimulation frequency). A change in fibre activation frequency may induce an increased synthesis of type II fibre myosin (fast myosin). Hormonal influences such as enhanced adrenergic stimulation of the muscle fibres cannot be excluded as a contributing factor, however.     

Calcium uptake and release modulated by counter-ion conductances in the sarcoplasmic reticulum of skeletal muscle

The sarcoplasmic reticulum (SR) plays the central role in regulating the free myoplasmic Ca²⁺ level for the contractile activation of skeletal muscle. The initial stages of the voltage-controlled Ca²⁺ release mechanism are known in molecular detail. However, there is still very little known about the later stages of Ca²⁺ uptake and total Ca²⁺ turnover in the contraction–relaxation cycle under normal physiological conditions or under conditions influenced by fatigue or disease. Ca²⁺ uptake and release are both accompanied by ‘counter-ion’ movements across the SR membrane which prevent or reduce the generation of SR membrane potentials and balance for electroneutrality in the SR lumen. The SR membrane is permeable for the cations K⁺, Na⁺, H⁺ and Mg²⁺ and the anion Cl^-. Using electron-probe X-ray microanalysis, it has been shown that during tetanic stimulation the Ca²⁺ release was mainly balanced by uptake of K⁺ and Mg²⁺, leaving a charge deficit that was assumed to be neutralized via H⁺ ion or organic counter-ion movement. The low time resolution of electron-probe X-ray microanalysis leaves the possibility of other transient concentration changes in the SR, e.g. for Cl^- ions. Possible physiological roles of the SR counter-ion conductances can be tested using skinned muscle fibre preparations with intact sarcoplasmic reticulum and removed or chemically permeabilized outer sarcolemma. In skinned fibres, the SR K⁺ conductance can be effectively reduced with SR K⁺ channel blockers such as 4-aminopyridine, tetraethylammonium and decamethonium. Interestingly, these blockers increase Ca²⁺ loading as well as Ca²⁺ release, whereas other less specific blockers, such as 1.10-bis-quanidino-n-decane, seem to reduce Ca²⁺ release, possibly also via blocking Ca²⁺ release channels. Thus, it seems very important also to test the effects of counter-currents carried by K⁺, Mg²⁺, H⁺ or Cl^- ions on intact and voltage-clamped single-fibre preparations.