Intracellular pH increase accompanies parthenogenetic activation of porcine, bovine and murine oocytes

Abstract

Although an intracellular pH (pH _i ) increase at the time of fertilization is necessary for activation of the sea urchin egg, recent reports in the mouse and rat have indicated that there is not a pH_i increase during fertilization or during 7% ethanol activation in the mouse. It has been suggested that mammals may have lost the need for a pH _i increase at the time of fertilization and the present study reports significant pH _i changes during parthenogenetic activation of porcine IVM oocytes, as well as pH _i responses to activation in bovine and murine oocytes. Transient intracellular pH changes were found during porcine oocyte activation when using 7% ethanol and with 50 or 100 M calcium ionophore (A23187). Treatment with 200 M thimerosal resulted in an increase in pH _i after a delay of approximately 12 min. Murine oocytes showed a significant increase during activation with 7% ethanol and A23187 as well as during prolonged exposure to thimerosal. Bovine oocytes exhibited an increase in pH _i only when activated with 50 or 100 M A23187. The final set of experiments aimed to determine whether the porcine oocyte has mechanisms to alleviate induced acidic and alkaline challenges. Both acidic (~20 mM acetic acid) and alkaline (~30 mM ammonium chloride) challenges caused significant changes in pH _i that porcine IVM oocytes were capable of recovering from within 35 min. Future studies will focus on determining which of the mechanisms is producing the pH _i increase at the time of parthenogenetic activation in the porcine oocyte.