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At least 631 records · Page 35Linked to original sources
PubMed1995

Modulation of a potassium conductance in developing skeletal muscle.

K+ conductances dominate and potentially modulate the resting potential of skeletal muscle cells. The expression and modulation of a major K+ conductance were examined during in vitro differentiation of the mouse myoblast cell line C2C12. The inwardly rectifying K+ conductance (IKi) increased from unmeasurable levels in undifferentiated myoblasts to approximately 1.56 +/- 0.51 nA (n = 17) in myoballs derived from myotubes at 5 days after induction of differentiation. The inward rectifier was subject to modulation by intracellular signals. Exposure of cytoplasm to guanosine 5'-O-(3-thiotriphosphate) during whole cell recording produced a concentration (5-100 microM)- and time (1-20 min)-dependent inhibition of the mean conductance. Elevation of intracellular free Ca2+ (> 200 nM) also inhibited IKi. These findings demonstrate a potential mechanism for modulation of the resting potential of muscle fibers via the control of skeletal muscle IKi.

Animals↗
PubMed2000

Effects of spaceflight and thyroid deficiency on hindlimb development. I. Muscle mass and IGF-I expression.

Thyroid deficiency (TD) in neonatal rats causes reduced growth of skeletal muscle that is disproportionately greater than that for other tissues (G. R. Adams, S. A. McCue, M. Zeng, and K. M. Baldwin. Am. J. Physiol. Regulatory Integrative Comp. Physiol. 276: R954-R961, 1999). TD depresses plasma insulin-like growth factor I (IGF-I) levels, suggesting a mechanism for this effect. We hypothesized that TD and exposure to spaceflight (SF) would interact to reduce skeletal muscle growth via a reduction in IGF-I levels. Neonatal rats were flown in space for 16 days. There was a similar, nonadditive reduction in the growth of the body ( approximately 50%) and muscle weight (fast muscles, approximately 60%) with either TD or SF. In the soleus muscle, either SF or TD alone resulted in growth reductions that were augmented by SF-TD interactions. There were strong correlations between 1) muscle mass and muscle IGF-I levels and 2) circulating IGF-I and body weight. These results indicate that either hypothyroidism or exposure to SF will limit the somatic and muscle-specific growth of neonatal rats. The impact of these perturbations on skeletal muscle growth is relatively greater than the effect on somatic growth. The mechanisms by which either TD or SF impact growth appear to have a common pathway involving the control of plasma and muscle IGF-I concentrations.

Animals↗
PubMed1988

[Calpains, protein kinase c and development of muscle tissue].

Calpains are Ca2+ -dependent thiol proteases which have been identified in various tissues of eucaryotes, but their physiological function in the cell is uncertain. In the muscle fiber, two types of calpains are present which differ by their calcium sensitivity: calpain 1 and calpain 2, which require for their activity micro and millimolar concentrations of calcium respectively. These calpains are associated with protein kinase C activities in the differentiated fiber. The multinucleate myotube is formed by fusion of mononucleated precursor cells, myoblasts. Calpains have been reported to appear in myoblasts at around the time of fusion. Moreover, an apparent synthesis of 1,2 diacylglycerol, an activator of protein kinase C, was observed during fusion of myoblasts. However, more information is required to incriminate totally protein kinase C and calpains in the mechanism of myoblast fusion.

Animals↗
PubMed1987

Adult forms of the Ca2+ATPase of sarcoplasmic reticulum. Expression in developing skeletal muscle.

Two separate genes encode fast-twitch and slow-twitch/cardiac muscle forms of the Ca2+ ATPase of sarcoplasmic reticulum. Full length Ca2+ ATPase clones have been isolated from adult rabbit fast-twitch, slow-twitch, and cardiac muscles. Segments of these clones containing unique sequences have been used as probes to study developmental changes in Ca2+ ATPase transcripts. The fast-twitch Ca2+ ATPase transcript undergoes developmentally regulated alternative splicing in which a penultimate 42-base pair exon is retained in the adult transcript but is excised in the neonatal transcript. This additional exon shifts the exon encoding the neonatal carboxyl-terminal sequence, -Asp-Pro-Glu-Asp-Glu-Arg-Arg-Lys (Brandl, C. J., Green, N. M., Korczak, B., and MacLennan, D. H. (1986) Cell 44, 597-607) into a nontranslated region and results in the expression of an adult isoform with a carboxyl-terminal -Gly. The neonatal form of the fast-twitch Ca2+ ATPase represents 72% of the fast-twitch Ca2+ ATPase transcripts just prior to birth but only 17% by 14 days of age and 4% in adult fast-twitch muscle. Adult slow-twitch, adult cardiac, and neonatal skeletal muscles express an identical Ca2+ATPase mRNA transcript which is distinct from either of the fast-twitch forms. The slow-twitch/cardiac Ca2+ ATPase is the predominant form expressed in late fetal and early neonatal rabbit skeletal muscle, but this form is lost as the skeletal muscle differentiates into a fast-twitch state. Three or more alternative polyadenylation signals exist for this mRNA in all tissues with the most 3' signal predominating.

Aging↗
PubMed1984

The effect of selective, chronic stimulation on motor unit size in developing rat muscle.

One of the two peripheral nerves which innervate rat lumbrical muscle was stimulated chronically in vivo during the postnatal period of synapse elimination to determine whether the differential stimulation would affect the outcome of the elimination process. Rats were anesthetized for about 4 hr a day for 5 to 6 consecutive days, during which time the sural nerve (or, in other animals, the lateral plantar nerve) was electrically stimulated. Each animal received about 10(6) stimuli. After the last stimulation period, the sizes of motor units in both nerves were estimated from motor unit tension recorded in vitro. We found that, on average, sural motor units were larger than others in animals which had received sural nerve stimulation and smaller than others in animals which had received lateral planter nerve stimulation. These results are consistent with the hypothesis that more active nerve terminals possess a relative advantage in competing for occupancy of the endplate.

Animals↗
PubMed1983

Growth and development of muscle fibres in the rainbow trout (Salmo gairdneri).

The growth of red and white muscle was investigated in the rainbow trout, using fish from 2.2 cm to 71 cm in length. In the white muscle, fibre hyperplasia, initially, accounted for all muscle growth but its relative contribution decreased as the contribution from fibre hypertrophy increased. At and above about 65 cm there was no hyperplasia, and this corresponded approximately to the stage when there were no more fibres in the smallest size class (less than 20 microns). The results for the red muscle are more variable and hence more difficult to assess. Although red fibre hyperplasia may continue throughout growth, at 34 cm there are no fibres in the smallest size class, which possibly indicates no new fibre formation beyond this stage.

Animals↗