The Role of Steroids, Growth Factors and CAMP Stimulators on the Gap Junction Activity in Cumulus Oocyte Complexes in the Rat
Bidirectional communication between mammalian oocytes and their surrounding somatic cells is essential for oocyte maturation. Gap junctions promote the transfer of essential metabolites, nucleotides, amino acids and ions from cumulus cells to the oocyte that are crucial for oocyte growth and development. However, the range of factors present in the microenvironment of the developing antral follicle, which modulate gap junction activity of the cumulus-oocyte complexes (COCs), is largely unknown. The primary objective of this study was to determine the effects of various steroids, growth factors and cAMP stimulators on the gap junction activity in rat COCs. The gap junction activity was measured in presence or absence of different treatments using a fluorescence dye and in the presence of milrinone, a phosphodiesterase type 3 inhibitor. The major findings of this study were that cAMP stimulators increased the rate of dye transfer from cumulus cells to the oocyte. Under in vitro conditions it was established that neither steroids nor IGF1 by themselves were able to modulate gap junction activity in rat COCs. Furthermore, forskolin, a potent cAMP stimulator; caused a relative increase in Cx37 gene expression levels following a four hours incubation period. The outcomes from the present study may help to provide new insights into developing suitable in vitro conditions, for the in vitro maturation of mammalian oocytes.