Normal (line 200) and dystrophic (line 307) embryonic chicken pectoralis muscle cells were studied in cell culture over a period of 2 weeks. During the first 4 days, normal and dystrophic cultures exhibited similar developmental increases in the number of nuclei within multinucleated myotubes, however, dystrophic muscle cells degenerated approximately twice as fast as normal cells once the initial burst of myoblast fusion was complete. The apparent synthesis rate of nonmyofibrillar proteins was similar in normal aand dystrophic cells throughout development, but the apparent synthesis rates of myosin heavy chain and the myofibrillar protein fraction were 50%--90% higher in dystrophic muscle cultures once maturity had been reached (days 6--14). The specific activities of creatine kinase and phosphofructokinase were not affected by the dystrophic condition; however, specific activity of AMP-deaminase was depressed 25%--40% in the dystrophic muscle cultures.

AMP Deaminase↗

PubMedDate not supplied

Normal and dystrophic embryonic chicken pectoralis muscle cultures: II. Ultrastructural comparison.

Ultrastructural comparison was made between dystrophic and normal chicken breast muscle cells which had been isolated from 12-day-old embryos and cultured for up to 14 days. All electron microscopic examinations were conducted in the absence of any knowledge as to the dystrophic or normal origin of the cells, or the day on which the cells had been harvested from culture. The same blind procedures were applied to attempts to reconstruct from electron micrographs the correct sequence of days for a particular experiment and to identify the origin of the cells as normal or dystrophic. No consistent differences between normal and dystrophic cells were apparent either in extent of differentiation, such as the formation of mature sarcomeres, or in degenerative properties, such as disintegrating mitochondria, lipid aggregations, or extracellular debris. In light of metabolic and developmental differences in these cultures, the absence of ultrastructural differences was attributed in part to the presence of cells with widely different degrees of integrity, differentiation, and degeneration in both normal and dystrophic cultures.

Animals↗

PubMedDate not supplied

Normal and dystrophic embryonic chicken pectoralis muscle cultures: III. Viral infection of normal cell cultures.

Twelve-day normal and dystrophic chick embryo breast muscle cells were cultured for up to 14 days, using normal embryo extract in the culture medium. Fluorodeoxyuridine was added on day 3 to suppress fibroblast overgrowth. Three of 6 experiments with normal cells were severely infected with avian leucosis/sarcoma (ALS) virus particles. The findings appear to lend support to the suggestion that the ALS virus is a mitochondriophage. Infected cultures demonstrated a depressed rate of total protein synthesis as reflected by incorporation of [3H]leucine. Extractable protein and total protein content were also depressed within several days after ALS particles were identified. These findings reinforce caution in acceptance of the common assumption that viral infections are an unavoidable and metabolically benign component of muscle cell cultures.

Alpharetrovirus↗

PubMedDate not supplied

beta-adrenergic receptor population is up-regulated by increased cyclic adenosine monophosphate concentration in chicken skeletal muscle cells in culture.

Skeletal muscle hypertrophy is promoted in vivo by administration of beta-adrenergic receptor (betaAR) agonists. Chicken skeletal muscle cells were treated with 1 microM isoproterenol, a strong betaAR agonist, between days 7 and 10 in culture. betaAR population increased by approximately 40% during this treatment; however, the ability of the cells to synthesize cyclic adenosine monophosphate (cAMP) was diminished by twofold. Neither the basal concentration of cAMP nor the quantity of myosin heavy chain (MHC) was affected by the 3-d exposure to isoproterenol. To understand further the relationship between intracellular cAMP levels, betaAR population, and muscle protein accumulation, intracellular cAMP levels were artificially elevated by treatment with 0-10 betaM forskolin for 3 d. The basal concentration of cAMP in forskolin-treated cells increased up to sevenfold in a dose-dependent manner. Increasing concentrations of forskolin also led to an increase in betaAR population, with a maximum increase of approximately 40-60% at 10 microM forskolin. A maximum increase of 40-50% in the quantity of MHC was observed at 0.2 microM forskolin, but higher concentrations of forskolin reduced the quantity of MHC back to control levels. At 0.2 microM forskolin, intracellular levels of cAMP were higher by approximately 35%, and the betaAR population was higher by approximately 30%. Neither the number of muscle nuclei fused into myotubes nor the percentage of nuclei in myotubes was affected by forskolin at any of the concentrations studied.

Adrenergic beta-Agonists↗