Effects of 20-week intermittent cold-water-immersion on phenotype and myonuclei in single fibers of rat hindlimb muscles

• Published in: Japanese journal of physiology Vol. 54; no. 4; p. 331
• Main Authors: Lee, J H, Han, E Y, Kang, M S, Kawano, F, Kim, H J, Ohira, Y, Kim, C K
• Format: Journal Article
• Language: English
• Published: Japan 01.08.2004
• Subjects: Animals; Body Weight; Cold Temperature; Hindlimb - physiology; Male; Muscle Fibers, Skeletal - physiology; Muscle Fibers, Skeletal - ultrastructure; Muscle, Skeletal - growth & development; Muscle, Skeletal - physiology; Myosin Heavy Chains - biosynthesis; Phenotype; Rats; Rats, Wistar; Weight Gain
• ISSN: 0021-521X
• DOI: 10.2170/jjphysiol.54.331

The effects of 20 weeks of intermittent cold-water-immersion on myosin heavy chain (MHC) expression,cross-sectional area (CSA), myonuclear number, and myonuclear domain size in isolated single fiber of soleus and extensor digitorum longus (EDL) muscles were studied in male Wistar rats. Cold exposure was accomplished by submerging the rats in shoulder-deep water, maintained at approximately 18 degrees C, for 1 hour/day, 5 days/week and for 20 weeks. Cold exposure resulted in a significant inhibition of body and soleus muscle weight gain. The percent type IIa MHC fibers of EDL muscle was increased, whereas that of type IIa + b MHC fibers was less in cold-exposed group than controls (p < 0.05). The mean CSA and myonuclear number in type I MHC fibers of soleus muscle in cold-exposed group were significantly less than controls. Myonuclear domain in type IIa fibers of EDL in the cold-exposed group was greater than controls (p < 0.05). It is suggested that prolonged cold exposure causes the fiber-type-specific adaptation in rat hindlimb muscles. It is further indicated that cold-exposure-related modulation of myonuclear number was closely related to reduction of fiber CSA, not the shift of fiber phenotype.