Relationships between myonuclear domain size and fibre properties in the muscles of Thoroughbred horses
Article first published online: 8 NOV 2010
© 2010 EVJ Ltd
Equine Veterinary Journal
Special Issue: Proceedings of the 8th International Conference on Equine Exercise Physiology
Volume 42, Issue Supplement s38, pages 311–316, November 2010
How to Cite
KAWAI, M., KUWANO, A., HIRAGA, A. and MIYATA, H. (2010), Relationships between myonuclear domain size and fibre properties in the muscles of Thoroughbred horses. Equine Veterinary Journal, 42: 311–316. doi: 10.1111/j.2042-3306.2010.00236.x
- Issue published online: 8 NOV 2010
- Article first published online: 8 NOV 2010
- [Paper received for publication 19.01.10; Accepted 21.06.10]
- myonuclear domain;
- fibre type;
- single fibre
Reasons for performing study: The myonuclear domain (MND) is the region of cytoplasm governed by a single myonucleus. Myonuclear domain size is an important factor for muscle fibre plasticity because each myonucleus has limitations in the capacity of protein synthesis. Previous studies have demonstrated that differences in MND size exist in different fibre types in several species, including horses.
Objectives: To understand the basic mechanism of muscle plasticity, the relationships between MND size, muscle fibre type population and metabolic properties of skeletal muscles throughout the whole body in Thoroughbred horses were examined.
Methods:Post mortem samples were taken from 20 muscles in 3 Thoroughbred horses aged 3–5 years of age. Fibre type population was determined on serial cross sections of each muscle sample, stained for monoclonal antibodies to each myosin heavy chain isoform. Oxidative (succinic dehydrogenase; SDH) and glycolytic (phosphofructokinase; PFK) enzyme activities were determined spectrophotometrically in each muscle sample. Furthermore, 30 single fibres were isolated from each muscle under stereomicroscopy and then fibre volume and myonuclear number for a given length analysed under confocal microscopy. The MND size of each single fibre was measured after normalisation of sarcomere length to 2.8 µm by staining with membrane-specific dye.
Results: Immunohistochemical staining indicated that soleus, vastus lateralis and gluteus medius muscles had the highest percentage of type I, IIa and IIx muscle fibre, respectively. Biochemical analysis indicated highest activities of SDH and PFK in diaphragm and longissimus lumborum muscles, respectively. MNDs were largest in the splenius muscle and smallest in the soleus and masseter muscles. Myonuclear domain size is significantly related to type I muscle fibre population, but not to SDH activities of the muscles.
Conclusion: The MND size of muscle fibre depends on fibre type population rather than mitochondrial enzyme activities.