Electrical pulse stimulation: an in vitro exercise model for the induction of human skeletal muscle cell hypertrophy. A proof-of-concept study

Abstract

Electrical Pulse Stimulation (EPS) of muscle cells has previously been used as an in vitro exercise model. The present study aims to establish an EPS protocol promoting the hypertrophy of human muscle cells, which represents a major physiological endpoint to resistance exercise in humans. We hypothesized that adding a resting period after EPS would be critical for the occurrence of the morphological change. Myoblasts obtained from human muscle biopsies (n = 5) were differentiated into multinucleated myotubes and exposed to 8 h EPS consisting of 2 ms pulses at 12 V with a frequency of 1 Hz. Myotube size was assessed using immunohistochemistry immediately, 4 h and 8 h after completed EPS. Gene expression and phosphorylation status of selected markers of hypertrophy were assessed using RT-PCR and western blotting, respectively. Release of the myokine IL-6 in culture medium was measured using ELISA. We demonstrate a significant increase (31 ± 14%; P = 0.03) in the size of myotubes when EPS is followed by 8 h resting period, but not immediately or 4 h after completed EPS. The response was supported by downregulation (P = 0.04) of myostatin gene expression, a negative regulator of muscle mass and increased phosphorylated mTOR (P = 0.03) and 4E-BP1 (P = 0.01), which are important factors in the cellular growth signalling cascade. The present work demonstrates that EPS is an in vitro exercise model promoting the hypertrophy of human muscle cells, recapitulating a major physiological endpoint to resistance exercise in human skeletal muscle.

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