Measures of Growth Processes and Myogenesis in Glycolytic and Oxidative Muscle Fibers in Rats after Indirect Electrical Stimulation

We report here a comparative study of activity in signal pathways and gene expression in the red (RGM) and white (WGM) parts of the gastrocnemius muscle in rats after series of short (1 sec) tetanic contractions evoked by stimulation of the motor nerve at a frequency of 100 Hz and an amplitude sufficient to activate all the motor units of the muscle. At 2 h after stimulation, WGM showed more marked increases in the level of ERK1/2 phosphorylation than RGM, though increases in AMPK phosphorylation were no different. Furthermore, the increases in MyoD and myogenin mRNA in WGM were significantly greater than those in RGM, while the effects of stimulation on expression of the IGF-1, MaFbx, and MuRF genes were weak and similar in WGM and RGM. There was also an increase in the content of myostatin mRNA in RGM. Thus, glycolytic muscle fibers in WGM display more marked regulatory hypertrophic-type shifts than the oxidative muscle fibers making up RGM.