Fig. 2

Long-term pacing disrupted the contractile structure of cardiomyocytes. a Compared with age-matched controls, the paced VCMs demonstrated decreased expression of cTnT, while cells from both the pacing and control groups showed robustly expressed Cx43 (scale bar 50 μm). TEM investigation illustrated significantly increased intracellular empty vacuoles and decreased myofibril density in paced VCMs (EV empty vacuoles, MF myofibrils, MI mitochondria, scale bar 500 nm, Myofibril panel, b); pacing also significantly increased the swelling mitochondria percentage, c; endoplasmic reticula (ER) with narrow cisterns were observed in the controls. By contrast, the paced VCMs demonstrated significantly increased aberrant dilated electron-dense ERs, which were swollen into circular shapes (^*endoplasmic reticulum, scale bar 500 nm, ER panel, b); qRT-PCR investigation revealed that the expression of TNNT2 was significantly lower in the pacing groups compared with the age-matched controls. However, the expression of Cx43 demonstrated a similar level among 40% Pace, 100% Pace and control VCMs (d). ^** p < 0.005, ^*** p < 0.001 according to a one-way ANOVA test