Short-duration electrical pulse stimulation induces myokines and mitochondrial adaptations in C2C12 myotubes
摘要
Physical activity induces rapid myokine and metabolic responses in skeletal muscle, yet the immediate cellular adaptations to short-duration contractile activity remain incompletely defined. C2C12 myotubes were exposed to electrical pulse stimulation (EPS; 40 V, 2 ms, 1 Hz) for 1 h and 2 h to evaluate time-dependent responses. A subset of cells was treated with AICAR (0.5 mM for 24 h or 1 mM for 2 h) to examine whether direct AMPK activation reproduces contraction-like effects. Cell viability, fiber-type markers, IL-6 and brain-derived neurotrophic factor (BDNF) secretion, glucose uptake, mitochondrial membrane potential (ΔΨm), mitochondrial DNA (mtDNA) abundance, and AMPK/PGC-1α signaling were assessed. EPS did not alter cell viability or fiber-type markers within 2 h. EPS increased IL-6 mRNA and IL-6 secretion, and significantly elevated BDNF secretion in the culture supernatants at 2 h. Glucose uptake increased over time (p for trend = 0.001). mtDNA abundance increased at 1 h (p < 0.05) and further at 2 h (p < 0.001), whereas ΔΨm showed a modest linear trend (p for trend = 0.046). AMPK phosphorylation increased progressively (p for trend < 0.001), accompanied by an emerging, non-significant increase in PGC-1α mRNA. AICAR activated AMPK and increased IL-6 secretion but did not alter BDNF levels, indicating partial overlap with EPS-induced signaling. Collectively, short-duration EPS elicits coordinated early myokine, metabolic, and mitochondrial responses in C2C12 myotubes, while pharmacological AMPK activation recapitulates IL-6 but not BDNF secretion, suggesting that contraction-specific signals cooperate with AMPK to regulate BDNF secretion.