2004 Volume 54 Issue 4 Pages 331-337
The effects of 20 weeks of intermittent cold-water-immersion on myosin heavy chain (MHC) expression,cross-sectional area (CSA), myonuclear number, andmyonuclear domain size in isolated single fiber of soleusand extensor digitorum longus (EDL) muscles were studied inmale Wistar rats. Cold exposure was accomplished bysubmerging the rats in shoulder-deep water, maintained at∼18°C, for 1 hour/day, 5 days/week and for 20 weeks.Cold exposure resulted in a significant inhibition of bodyand soleus muscle weight gain. The percent type IIa MHCfibers 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 intype I MHC fibers of soleus muscle in cold-exposed groupwere significantly less than controls. Myonuclear domain intype IIa fibers of EDL in the cold-exposed group was greaterthan controls (p < 0.05). It is suggested thatprolonged cold exposure causes the fiber-type-specificadaptation in rat hindlimb muscles. It is further indicatedthat cold-exposure-related modulation of myonuclear numberwas closely related to reduction of fiber CSA, not the shiftof fiber phenotype.
