Effects of electromyostimulation on sarcolipin and Ca²⁺ signaling in rat skeletal muscles

Calcium ion (Ca²⁺) acts as a second messenger involved in various adaptations by activating signaling pathways. The expression of Ca²⁺ regulators is modified by resistance training. Thus, Ca²⁺ signaling may be altered during a period of resistance training. In this study, male Sprague-Dawley rats underwent repeated resistance exercise via transcutaneous electromyostimulation, and the expression of Ca²⁺-related factors was examined 3 h after the 1st, 5th, and 10th exercise sessions. Expression of sarcolipin (SLN) and regulator of calcineurin 1 (RCAN1) was significantly higher in exercised legs than control legs after the 5th (p < 0.001) and 10th sessions (p < 0.001). Calcineurin expression showed significant main effects of exercise (p = 0.009) and session (p < 0.001). A significant main effect of session was also observed for Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) (p < 0.001), CaMKII α (p < 0.046), CaMKII β (p = 0.002), and CaMKII γ (p < 0.001). In contrast, expression of sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) did not change with repeated electromyostimulation. Pearson's correlation analysis showed a significant positive correlation between the expression of SLN and RCAN1 (r = 0.630, p = 0.005) and between SLN and CaMKII γ (r = 0.471, p = 0.048), as well as a trend for a positive correlation between SLN and CaMKII (r = 0.463, p = 0.053). These results suggest that repeated sessions of electromyostimulation increase SLN expression, which may in turn contribute to enhanced Ca²⁺ signaling after exercise.