Hypertrophy of mature Xenopus muscle fibres in culture induced by synergy of albumin and insulin

• Published in: Pflügers Archiv Vol. 457; no. 1; pp. 161 - 170
• Main Authors: Jaspers, R. T., van Beek-Harmsen, B. J., Blankenstein, M. A., Goldspink, G., Huijing, P. A., van der Laarse, W. J.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-10-2008; Springer Nature B.V
• Subjects: Adenosine Triphosphatases - metabolism; Albumins - pharmacology; Animals; Biomedical and Life Sciences; Biomedicine; Cell Biology; Cells, Cultured; Cytoplasm - drug effects; Cytoplasm - metabolism; Densitometry; Diffusion Chambers, Culture; Female; Glycogen - metabolism; Human Physiology; Hypertrophy; Hypoglycemic Agents - pharmacology; Immunohistochemistry; Insulin - pharmacology; Lipids - chemistry; Mitochondria, Muscle - drug effects; Mitochondria, Muscle - enzymology; Molecular Medicine; Muscle Contraction - drug effects; Muscle Fibers, Skeletal - drug effects; Muscle Fibers, Skeletal - physiology; Muscle Fibers, Skeletal - ultrastructure; Muscle Physiology; Muscular system; Myofibrils - drug effects; Myofibrils - enzymology; Neurosciences; Receptors; Sarcomeres - drug effects; Sarcomeres - ultrastructure; Xenopus laevis; Albumin; Skeletal muscle fibre; Insulin; Adaptation; Hypertrophy
• ISSN: 0031-6768; 1432-2013
• DOI: 10.1007/s00424-008-0499-0

The aim of this study was to investigate effects of albumin and insulin separately as well as in combination on mature muscle fibres during long-term culture. Single muscle fibres were dissected from m. iliofibularis of
Xenopus laevis
and attached to a force transducer in a culture chamber. Fibres were cultured in a serum-free medium at slack length (mean sarcomere length 2.3 μm) for 8 to 22 days. The medium was supplemented with (final concentrations): (1) bovine insulin (6 nmol/L or 200–600 nmol/L), (2) 0.2% bovine albumin or (3) 0.2% bovine albumin in combination with insulin (120 nmol/L). In culture medium with insulin, 50% of the muscle fibres became in-excitable within 7–12 days, whereas the other 50% were stable. Caffeine contractures of in-excitable muscle fibres produced 80.4 ± 2.4% of initial peak tetanic force, indicating impaired excitation–contraction (E–C) coupling in in-excitable fibres. In the presence of albumin, all cultured muscle fibres were stable for at least 10 days. Muscle fibres cultured in medium with insulin or albumin exclusively did not hypertrophy or change the number of sarcomeres in series. In contrast, muscle fibres cultured with both albumin and insulin showed an increase in tetanic force and fibre cross-sectional area of 19.6 ± 2.8% and 32.5 ± 4.9%, respectively, (means ± SEM.;
P
 = 0.007) after 16.3 ± 1.7 days, whereas the number of sarcomeres in series remained unchanged. We conclude that albumin prevents muscle fibre damage and preserves E–C coupling in culture. Furthermore, albumin is important in regulating muscle fibre adaptation by a synergistic action with growth factors like insulin.