Frequency Of Satellite Cells Research Articles

Morphological observations supporting muscle fiber hyperplasia following weight-lifting exercise in cats.

Although exercise-induced muscle fiber hyperplasia has been demonstrated through direct fiber counts following nitric-acid digestion of muscle, morphological studies to determine the mechanism of hyperplasia have not been performed previously. In this study, light and electron microscopy were used to evaluate evidence of muscle fiber splitting or de novo formation of new muscle fibers. Since both fiber hypertrophy and hyperplasia may result in alterations in the muscle nuclear populations, myonuclear number and satellite cell frequency were assessed quantitatively to determine their role in regulating muscle fiber size. Ten adult cats performed weight-lifting exercise, and the right (exercised) and left (control) forelimbs were fixed by vascular perfusion. Spaced serial sections were used to evaluate muscle fiber morphology along the length of fibers, and muscle fiber areas were measured. Myonuclei and satellite cells were counted using electron microscopy. Morphological evidence supporting muscle fiber hyperplasia was observed in exercised muscles. These observations included the presence of small fibers which may signify de novo fiber formation. Myonuclear counts indicate that myonuclear density is not a primary regulator of fiber size. Satellite cell frequency was unchanged following exercise. Autoradiographic studies revealed satellite cell activation by uptake of tritiated thymidine in exercised muscles. Satellite cell activation appears to result from increased activity in exercised muscles. These findings confirm previous studies demonstrating muscle fiber hyperplasia following weight-lifting exercise, and suggest that de novo fiber formation is the major mechanism contributing to muscle fiber hyperplasia in this model.

A quantitative study of satellite cells and myonuclei in stretched avian slow tonic muscle.

Satellite cell frequency was assessed in control and stretched anterior latissimus dorsi (ALD) muscles of adult quail. A weight equal to 10% of body mass was attached to one wing for time intervals ranging from 1-30 days. The contralateral ALD served as the intra-animal control. Satellite cell frequency, expressed as a percentage of total myofiber nuclei within the basal lamina, was determined in eight control and stretched ALD muscles, that had been weighted for 5, 7, or 10 days. Satellite cell frequency was determined in 584 control and 473 stretched fibers and was not different in the control or stretched ALD muscles (15.6 +/- 2.3%, 16.7 +/- 6.1%, respectively). The number of myofiber nuclei (myonuclei and satellite cell nuclei) was examined in whole fiber segments from control and stretched ALD muscles of 27 adult quail. Nuclear frequency was determined in 500 control and 1,200 stretched fiber segments. Fiber volume was calculated from fiber length and diameter measurements. Nuclear number normalized to 10,000 microns 3 fiber volume was correlated to fiber cross-sectional area (P less than 0.0001). Fibers with cross-sectional areas less than 500 microns 2 had a greater nuclear to fiber volume ratio compared to fibers with areas greater than 500 microns 2. The nuclear-to-cytoplasmic ratio was not constant in smaller fibers. Nuclear density decreased as fiber cross-sectional area increased up to 500 microns 2. Fibers with cross-sectional areas greater than 500 microns 2 demonstrated a constant nuclear-to-cytoplasmic ratio. The results demonstrate that absolute nuclear number increased to maintain a constant nuclear-to-cytoplasmic ratio in the stretched hypertrophied fibers. Daughter cells originating from activated satellite cells may have contributed to the myonuclear population to maintain a constant nuclear-to-cytoplasmic ratio in the hypertrophied fibers of the adult quail.

Satellite cell response in rat soleus muscle undergoing hypertrophy due to surgical ablation of synergists

Although the role of satellite cells has been confirmed during skeletal muscle growth and regeneration, their involvement during work-induced muscle growth remains uncertain. In this study, chronically overloaded rat soleus muscles were ultrastructurally monitored following surgical ablation of synergists to examine cytological adaptations of satellite cells and myofibers. The left soleus muscle of 20 female Sprague-Dawley rats (7 weeks of age) was induced to hypertrophy by excising the contralateral plantaris and gastrocnemius muscles under pentobarbital anesthesia. Right limbs were sham-operated and served as controls. On days 3, 7, 14, 21, and 30 after surgery, the soleus muscles were removed and processed for electron microscopy. Two morphologically distinct phases were noted in the surgically overloaded muscles. The first stage (week 1) was characterized by a significant increase in the number of satellite cells, and by more than half of the experimental muscle fibers displaying myofibrillar disruptions, mitochondrial alterations and glycogen pooling. The second phase (weeks 2-4) featured mostly normal, although larger appearing muscle fibers, with the satellite cell frequency remaining slightly elevated. These findings suggest that muscle fiber structural abnormalities, rather than an increase in muscle activity, may play a more significant role in the early activation of satellite cells during compensatory hypertrophy, whereas activation of satellite cells during the later stages may be in response to increased levels of muscle activity.

Satellite cell distribution within the soleus muscle of the adult mouse.

The frequency of satellite cells was quantitated by electron microscopy in five proximal to distal regions of the soleus muscle of adult mice. In all, 236 satellite cell nuclei and 4, 475 myonuclei were counted on 51 transverse thin sections. The mean percentage of satellite cells, as a ratio of satellite cells to myonuclei, per region was found to be 5.4%, 5.3%, 5.0%, 5.2% and 4.9% for the most proximal to distal areas, respectively. Analysis of variance revealed no significant differences between either the regions or the animals studied. The number of satellite cell nuclei per cross-sectional area of muscle was also calculated for each of the five regions, and these values did not vary significantly from the proximal to distal ends of the muscle. Despite the fact that satellite cells were frequently noted in close association with cross-sectional profiles of myoneural junctions, this study establishes that the number of such perisynaptic satellite cells was not large enough to affect significantly the mean percentages of all satellite cells counted within the motor endplate regions(areas 3 and 4) of the soleus muscle. It is concluded from this study that satellite cells are uniformly distributed throughout the whole muscle.

Satellite cells in the latissimus dorsi of the rat.

This study was carried out with the aid of the electron microscope to determine the frequency of satellite cells in mammalian skeletal muscle fibre. 10 normal adult male albino rats were used and specimens from the latissimus dorsi muscle were removed, processed and prepared for electron microscope examination. Satellite cells were first identified by their location, shape and organelles. Counts were then carried out on 72 electron microscope fields at X 8,000 magnification from both longitudinal and transverse sections. The total number of nuclei was counted first, then the nuclei of satellite cells were identified and recorded. It has been found that satellite cell nuclei accounted for only 4.5% of all the nuclei seen. The rest being myonuclei within the muscle fibre. This surprisingly small number of satellite cells leaves the question of their role in muscle regeneration and that of the origin of the large numbers of 'myoblasts' that appear in the early stages of muscle repair after injury yet to be answered.

The satellite cells of normal anuran skeletal muscle

Population counts and size measurements of satellite cell nuclei and myonuclei were carried out on the normal gastrocnemius muscles of adult Rana pipiens and Rana clamitans. Satellite cell profiles occurred with an observed frequency of about 1.3% in the muscles of the R. pipiens, and with an observed frequency of about 1.6% in the muscles of the R. clamitans. These frequencies were not found to be significantly different. The observed frequencies were corrected for the sampling bias introduced by the difference in the mean size of the satellite cell nuclei and myonuclei. This correction suggests that R. pipiens and R. clamitans both have a true satellite cell frequency of approx 2.7%. Analysis of these data indicates that the satellite cells of the normal anuran gastrocnemius occur in sufficient numbers to account for the regeneration seen after injury to this muscle.