Differences in energy metabolism and neuromuscular transmission between 30-Hz and 100-Hz stimulation in rat skeletal muscle

Objective: To examine differences in energy metabolism and neuromuscular tr ansmission failure in rat hindlimb muscles subjected to electric stimulatio n at different frequencies. Design: Experimental animal study. Setting: Bioenergetic Research Center at Otsuka Pharmaceutical Company, Ots uka, Japan. Animals: Thirty-two 25-week-old male Wistar-Kyoto rats. Interventions: With the rat under general anesthesia, the sciatic nerve was electrically stimulated at 30Hz and 100Hz to induce muscle contraction. Main Outcome Measures: Energy level and intracellular pH of muscles by phos phorus-31 magnetic resonance spectroscopy (P-31-MRS); M-wave amplitude of m uscles by electromyography. Results: During the first 4 minutes under stimulation at 30Hz and at 100Hz, energy level and intracellular pH dropped to their lowest values (p < .05 or p < .01); the values then recovered with time. Recovery rates of energy level and intracellular pH during stimulation at 100Hz were greater than th ose observed during stimulation at 30Hz. The M-wave amplitude during 100-Hz stimulation was permanently and significantly lower than that measured dur ing 30-Hz stimulation(p < .01), and the recovery rate of M-wave amplitude a fter stimulation at 100Hz was slower than that after stimulation at 30Hz. Conclusion: Neuromuscular transmission failure was greater with 100-Hz stim ulation than with 30-Hz stimulation. This finding may account for the rapid recovery of energy level and intracellular pH that occurs with stimulation at 100Hz.