Analysis of the mitochondrial membrane potential (Δψm) and mPTP opening in the d-galactose age-induced primary cultured neonatal cardiomyocytes. a JC-1 measured the mitochondrial membrane potential (Δψm). The cells of different groups were stained with JC-1 probe and imaged by fluorescent microscope. JC-1 spontaneously forms J-aggregate and exhibits red fluorescence under a high potential. The JC-1 monomeric form shows green fluorescence under a low potential. The individual red and green average fluorescence intensities are expressed as the ratio of red to green fluorescence. b Changes of mPTP opening were measured with calcein-AM. The fluorescence intensity in control group were considered 100% viable. The changes of fluorescence intensity are inversely proportional with degree of the mPTP opening. All data were from four independent experiments. *p < 0.05 vs. control group; #p < 0.05 vs. H/R group; &p < 0.05 vs. PC group; $p < 0.05 vs. H/R + NaHS group; §p < 0.05 vs. PC + NaHS group.