Morphometric analysis of satellite cells in rat skeletal muscles: soleus and extensor digitorum longus

Functional properties of muscle-derived cells related to morphological characteristics

Satellite cells represent a specific lineage of myogenic progenitors that allow skeletal muscle postnatal growth and repair. They have been described as being heterogeneous in nature, a characteristic associated with functional disparities. Here, we aimed at determining whether the morphometric characteristics of freshly extracted turkey muscle-derived cells (MDC) could represent a distinctive criterion between them and could also be associated with their behavioural features. Morphometric analysis showed that MDC displayed wide cell size diversity, from 4 to 10 mum. Lineage marker analysis was performed on MDC sorted by their size using counterflow centrifugal elutriation and showed that the cell size was associated with the specific expression of myogenic markers, revealing different commitment levels. In vitro, the smallest MDC exhibited limited myogenic activity while larger MDC displayed a myogenic potential that increased with their size. Ultrastructural analysis revealed that the smallest MDC shared quiescent cell features, whereas the other cells displayed metabolic activity that also increased as a function of their size. Collectively, our results demonstrate that the size of freshly extracted MDC is indicative of their respective progression towards myogenic differentiation lineage. This criterion could be useful for the early separation of more or less committed cells in the myogenic programme.

Ca2+ cytochemical changes of hepatotoxicity caused by halothane and sevoflurane in enzyme-induced hypoxic rats

AIM: To investigat the relation between hepatotoxicity of halothane and sevoflurane and altered hepatic calcium homeostasis in enzyme-induced hypoxic rats.

METHODS: Forty-eight rats were pretreated with phen-obarbital and randomly divided into six groups (eight in each group) and exposed to O₂/ N₂/1.2 MAC anesthetics for 1 h: normal control (NC), 21% O₂/79% N₂; hypoxic control (HC), 14% O₂/86%N₂; normal sevoflurane (NS), 21% O₂/ N₂/1.2MAC sevoflurane; hypoxic sevoflurane (HS), 14% O₂/ N₂/1.2MAC sevoflurane; normal halothane (NH)21%O₂/79%N₂/1.2MAC halothane; hypoxic halothane (HH), 14% O₂/N₂/1.2MAC halothane. Liver specimens and blood were taken 24 h after exposure to calcium and determined by EDX microanalysis.

RESULTS: The liver of all rats given halothane (14% O₂) had extensive centrilobular necrosis and denaturation. Morphologic damage was accompanied with an increase in serum glutamic pyruvic transminase. In groups NH and HH, more calcium was precipitated in cytoplasm and mitochondria.

CONCLUSION: These results suggest that halothane increases cytosolic Ca²⁺ concentration in hepatocytes. Elevation in Ca²⁺ concentration is implicated in the mechanism of halothane-induced hepatotoxicity. sevoflurane is less effective in affecting hepatic calcium homeostasis than halothane.

Testosterone-induced muscle hypertrophy is associated with an increase in satellite cell number in healthy, young men

Testosterone (T) supplementation in men induces muscle fiber hypertrophy. We hypothesized that T-induced increase in muscle fiber size is associated with a dose-dependent increase in satellite cell number. We quantitated satellite cell and myonuclear number by using direct counting and spatial orientation methods in biopsies of vastus lateralis obtained at baseline and after 20 wk of treatment with a gonadotropin-releasing hormone agonist and a 125-, 300-, or 600-mg weekly dose of T enanthate. T administration was associated with a significant increase in myonuclear number in men receiving 300- and 600-mg doses. The posttreatment percent satellite cell number, obtained by direct counting, differed significantly among the three groups (ANCOVA P < 0.000001); the mean posttreatment values (5.0 and 15.0%) in men treated with 300- and 600-mg doses were greater than baseline (2.5 and 2.5%, respectively, P < 0.05 vs. baseline). The absolute satellite cell number measured by spatial orientation at 20 wk (1.5 and 4.0/mm) was significantly greater than baseline (0.3 and 0.6/mm) in men receiving the 300- and 600-mg doses (P < 0.05). The change in percent satellite cell number correlated with changes in total (r = 0.548) and free T concentrations (r = 0.468). Satellite cell and mitochondrial areas were significantly higher and the nuclear-to-cytoplasmic ratio lower after treatment with 300- and 600-mg doses. We conclude that T-induced muscle fiber hypertrophy is associated with an increase in satellite cell number, a proportionate increase in myonuclear number, and changes in satellite cell ultrastructure.

Mitotic activity of rat muscle satellite cells in response to serum stimulation: relation with cellular metabolism

Cellular and molecular adaptations of satellite cells isolated from rat hindlimb muscles (n = 10) were investigated in response to serum stimulation. Flow cytometry analysis of the amounts of DNA and RNA indicated that 97.7 +/- 0.7% of satellite cells were in G0 at the end of the isolation procedure, whereas 93.2 +/- 2.0% of cells were cycling after serum exposure. The length of cell division was 34.0 +/- 2.8 h. Myoblast proliferation was asynchronous, suggesting the existence of heterogeneous cell populations in skeletal muscle. Myoblast proliferation was also accompanied by a significant increase in c-met expression, and major adaptations of energetic and proteolytic metabolisms, including an increase in the relative contribution of glycolytic metabolism for energy production, an increase in proteasome and matrix metalloproteinases 2 and 9 activities, and a decrease in plasminogen activator activities. Our data suggest that, along with molecular adaptations leading to cell cycle activation itself, adaptations in energetic and proteolytic metabolisms are crucial events involved in satellite cell activation and myoblast proliferation.

Preconditioning with millimolar concentrations of vitamin C or N-acetylcysteine protects L6 muscle cells insulin-stimulated viability and DNA synthesis under oxidative stress

The effect of reactive oxygen/nitrogen species (ROS/RNS)(hydrogen peroxide -- H(2)O(2), superoxide anion radical O(2)*- and hydroxyl radical *OH -- the reaction products of hypoxanthine/xanthine oxidase system), nitric oxide (NO* from sodium nitroprusside -- SNP), and peroxynitrite (ONOO(-) from 3-morpholinosydnonimine -- SIN-1) on insulin mitogenic effect was studied in L6 muscle cells after one day pretreatment with/or without antioxidants. ROS/RNS inhibited insulin-induced mitogenicity (DNA synthesis). Insulin (0.1 microM), however, markedly improved mitogenicity in the muscle cells treated with increased concentrations (0.1, 0.5, 1 mM) of donors of H(2)O(2), O(2)*-, *OH, ONOO(-) and NO*. Cell viability assessed by morphological criteria was also monitored. Massive apoptosis was induced by 1 mM of donors of H(2)O(2) and ONOO(-), while NO* additionally induced necrotic cell death. Taken together, these results have shown that ROS/RNS provide a good explanation for the developing resistance to the growth promoting activity of insulin in myoblasts under conditions of oxidative or nitrosative stress. Cell viability showed that neither donor induced cell death when given below 0.5 mM. In order to confirm the deleterious effects of ROS/RNS prior to the subsequent treatment with ROS/RNS plus insulin one day pretreatment with selected antioxidants (sodium ascorbate - ASC (0.01, 0.1, 1 mM), or N-acetylcysteine - NAC (0.1, 1, 10 mM) was carried out. Surprisingly, at a low dose (micromolar) antioxidants did not abrogate and even worsened the concentration-dependent effects of ROS/RNS. In contrast, pretreatment with millimolar dose of ASC or NAC maintained an elevated mitogenicity in response to insulin irrespective of the ROS/RNS donor type used.