Fig. 6

Long-term pacing induced ER stress and calpain activity. Western blot (a) analysis demonstrated that the protein levels of both GRP78 and CHOP were markedly elevated after pacing compared to those in the age-matched controls (b), indicating the occurrence and exacerbation of ER stress. Consistently, it also demonstrated a significantly higher expression level of calpain in the paced VCMs than in the controls. The calpain activity was further investigated by an ELISA assay. The results revealed that pacing induced calpain activity in a Cum%VP-dependent manner (c). ^* p < 0.05, ^** p < 0.005, ^*** p < 0.001 according to a one-way ANOVA test