Effect of stimulation frequency on metabolism of skeletal muscles

We studied the effects of stimulation frequency on the energy metabolism of rat skeletal muscles during electrical low-frequency stimulation, using in vivo phosphorus-31 magnetic resonance spectroscopy. The sciatic nerve of Wistar-Kyoto rats (n = 16) was stimulated electrically using low frequency stimulation (LFS) at 30 Hz and high frequency stimulation (HFS) at 100 Hz as tetanizing frequencies. The initial tension during LFS was significantly different from that during HFS, 200.49 +/- 19.47 vs. 516.67 +/- 5.38 dynes (mean +/- S.E.; n = 8) (p < 0.01). In the first 2 min of stimulation, the ratio of phosphocreatine (PCr) to inorganic phosphate (Pi) + sugar phosphate (SP) during LFS and HFS were 0.28 +/- 0.04 and 0.53 +/- 0.06 (mean +/- S.E.; n = 8), respectively. Subsequently, the ratio during LFS remained lower than that during HFS. The intracellular pH during LFS and HFS in the first 2 min of stimulation was 6.27 +/- 0.02 and 6.75 +/- 0.03 (mean +/- S.E.; n = 8), respectively. From 2 min to 12 min of stimulation, the intracellular pH during LFS remained lower than that during HFS. The results showed that lower levels of both energy and intracellular pH of skeletal muscles were maintained during LFS than during HFS, facilitating aerobic glycolysis to produce ATP during stimulation.