Effect of vitrification on mitochondrial membrane potential in human metaphase II oocytes

The aim of this study was to evaluate the impact of vitrification on mitochondrial membrane potential (Delta Im) in human metaphase II (MII) oocytes, and the changes of Delta Im on thawed MII oocytes. MII oocytes were obtained from clinical IVF cycles when the oocytes were failed to fertilization within 24 h after insemination. All oocytes were randomly divided into 4 groups: non-frozen (fresh group), cultured for 0 h (0 h group), 2 h (2 h group) and 4 h (4 h group) after vitrification/thawing. All oocytes were stained with the Delta Im-specific probe JC-1 and detected by laser scanning confocal microscope (LSCM) for mitochondrial analysis. The Delta Im of oocytes was significantly decreased in 0 h and 2 h groups when compared with fresh group (0.93, 1.09 vs 1.34, P < 0.05), but similar between 4 h group and fresh group (1.30 vs 1.34, P > 0.05). In the vitrification/thawing process, the Delta Im of MII oocytes could have temporally dynamic changes within 2 h after thawing but would be fully recovered after 4 h culture.