Direct electrical stimulation of rat soleus during denervation-reinnervation

Abstract

The effect of direct, low-frequency electrical stimulation (at 10 Hz continuously 8 h daily) of muscle on isometric twitch contractile properties of adult rat soleus was observed during denervation and reinnervation. The normal and the bilaterally sciatic nerve crush-denervated groups were implanted with unilateral juxtamuscular electrodes to stimulate the soleus muscle in one limb. After 10, 15, 20, 25, and 30 days of electrical stimulation (2- to 4-mA pulses at 4 ms duration) the normal control, normal-stimulated, crush-denervated control, and crush-denervated-stimulated soleus muscles ( N = 6) were evaluated in vitro by massively field stimulating the muscles in physiologic buffer ( pH 7.2) at 23 to 24°C. The parameters of isometric twitch contraction measured were latent period (LP), maximum isometric twitch tension ( P t), contraction time (CT), maximum rate of isometric twitch tension ( V t max), and half-relaxation time (HRT). In normal muscle, 25 and 30 days of electrical stimulation produced significant ( P < 0.05) changes: muscle hypertrophy (26.5 and 16.6%, respectively), decline in the P t (23.4 and 12.1%, respectively), and decrease in the ( V t max) (17.3 and 21.6%, respectively). For the same periods, compared with the crush-denervated control, the crush-denervated-stimulated muscles also showed significant ( P < 0.05) changes: prolongation of the LP. (22.9 and 26.5%), decline in the P t (24.5 and 31.6%), and decrease in the V t max (27.7 and 33.3%). These results, therefore, suggest that the long-term (200 to 240 h) direct, lowfrequency (10 Hz) electrical stimulation may impair the mechanism of isometric twitch development in slow-twitch muscle of the rat. However, our study does not prove that this pattern of electrostimulation can significantly alter the course of self-reinnervation in muscle.