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

Abstract

Although an intracellular pH (pHi) 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 pHi increase during fertilization or during 7% ethanol activation in the mouse. It has been suggested that mammals may have lost the need for a pHi increase at the time of fertilization and the present study reports significant pHi changes during parthenogenetic activation of porcine IVM oocytes, as well as pHi 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 microM calcium ionophore (A23187). Treatment with 200 microM thimerosal resulted in an increase in pHi 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 pHi only when activated with 50 or 100 microM A23187. The final set of experiments aimed to determine whether the porcine oocyte has mechanisms to alleviate induced acidic and alkaline challenges. Both acidic (approximately 20 mM acetic acid) and alkaline (approximately 30 mM ammonium chloride) challenges caused significant changes in pHi 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 pHi increase at the time of parthenogenetic activation in the porcine oocyte.