INTRACELLULAR PH CHANGES DURING ZONA DRILLING

Objective: To investigate whether zona drilling of oocytes, a techniqu e used to locally disrupt the zona pellucida, causes important changes in intracellular pH. Design and Methods: In a first set of experiment s, intracellular pH was measured during zona drilling of mouse oocytes , using pH-sensitive microelectrodes. In a second set of experiments, human oocytes that failed to fertilize were used to measure intracellu lar pH during drilling. In these cells intracellular pH was measured u sing microfluorimetry with the pH-sensitive dye 2',7'-bis-carboxyethyl -5(6) -carboxyfluorescein. Results: In mouse oocytes intracellular pH dropped from 7.25 +/- 0.02 (mean +/- SEM) to 7.09 +/- 0.03 during zona drilling, followed by a recovery to pH 7.17 +/- 0.02 after 4 minutes (n = 20). In human oocytes, intracellular pH dropped over 0.36 +/- 0.1 0 pH units during drilling, followed by a recovery that was complete w ithin 4 minutes (n = 14). Conclusion: Zona drilling is associated with a significant cytoplasmic acidification both in mouse and human oocyt es. This effect is perhaps related to the high incidence of cytoplasmi c degeneration after zona drilling of human oocytes.