We studied the effects of stimulation frequency on the energy metabolism of rat skeletal muscles during electrical low-frequency stimulation by
in vivo Phosphorus-31 Magnetic Resonance Spectroscopy (
31P-MRS). For this, the sciatic nerve of Wistar-Kyoto rats (WKY) was stimulated electrically at 30Hz and 100Hz as tetanizing frequency. The initial tension at 30Hz was 201.1±21.0 dynes and that at 100Hz was 518.0±5.6 dynes, which was significantly different (p<0.01). Later, the tension produced at 30Hz and 100Hz decreased with time and was not significantly different. The phosphocreatine (PCr)/{inorganic phosphate (Pi)+sugar phosphate (SP)} indicates the energy level of skeletal muscles. In the first 2min of stimulation, the ratios at 30Hz and 100Hz were 0.3±0.1 and 0.5±0.1, respectively. Later, the ratios at 30Hz were maintained at lower values than those at 100Hz. In
31P-MRS spectra, SP peaks at 30Hz were higher than those at 100Hz. The intracellular pH at 30Hz and 100Hz in the first 2min of stimulation was 6.28±0.02 and 6.77±0.02, respectively. From 2min to 12min of stimulation, the intracellular pH at 30Hz was maintained at lower values than that at 100Hz.
The results showed that 30Hz-stimulation maintained lower levels of both energy and intracellular pH of skeletal muscles and facilitated aerobic glycolysis to produce ATP during stimulation, and suggest that 30Hz may be a more effective frequency of electrical low-stimulation than 100Hz to improve muscle atrophy and muscle weakness.
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