Low-intensity electrical stimulation ameliorates disruption of transverse tubules and neuromuscular junctional architecture in denervated rat skeletal muscle fibers

We determine the effects of direct electrical stimulation (ES) on the histological profiles in atrophied skeletal muscle fibers after denervation caused by nerve freezing. Direct ES was performed on the tibialis anterior (TA) muscle after denervation in 7-week-old rats divided into groups as follows: control (CON), denervation (DN), or denervation with direct ES (subdivided into a 4 mA (ES4), an 8 mA (ES8), or a 16 mA stimulus (ES16). The stimulation frequency was set at 10 Hz, and the voltage was set at 40 V (30 min/day, 6 days/week, for 3 weeks). Ultrastructural profiles of the membrane systems involved in excitation-contraction coupling, and four kinds of mRNA expression profiles were evaluated. Morphological disruptions occurred in transverse (t)-tubule networks following denervation: an apparent disruption of the transverse networks, and an increase in the longitudinal t-tubules spanning the gap between the two transverse networks, with the appearance of pentads and heptads. These membrane disruptions seemed to be ameliorated by relatively low intensity ES (4 mA and 8 mA), and the area of longitudinally oriented t-tubules and the number of pentads and heptads decreased significantly (P < 0.01) in ES4 and ES8 compared to the DN. The highest intensity (16 mA) did not improve the disruption of membrane systems. There were no significant differences in the alpha 1sDHPR and RyR1 mRNA expression among CON, DN, and all ES groups. After 3 weeks of denervation all nerve terminals had disappeared from the neuromuscular junctions (NMJs) in the CON and ES16 groups. However, in the ES4 and ES8 groups, modified nerve terminals were seen in the NMJs. The relatively low-intensity ES ameliorates disruption of membrane system architecture in denervated skeletal muscle fibers, but that it is necessary to select the optimal stimulus intensities to preserve the structural integrity of denervated muscle fibers.