Intracellular pH regulation in the human oocyte

Abstract

We have used fluorescence techniques to study the regulation of intracellular pH during fertilization and preimplantation embryo development in human oocytes. The intracellular pH of human oocytes during maturation and fertilization was always 7.4, suggesting that these processes do not involve long-term changes in intracellular pH. The recovery of intracellular pH of human oocytes and embryos after extracellular acid or alkaline shock was investigated. Fresh metaphase II oocytes and preimplantation embryos showed similar rates of recovery following alkaline shock. However, aged and immature oocytes had a significantly slower rate of recovery to physiological pH. Early embryos up to the morula stage were unable to recover following acidosis, whereas blastocysts could control both acidosis and alkalosis. We assessed the sensitivity of fertilization and early development in the human to extracellular pH. Our results show that insemination in the human is pH-sensitive, whereas intracytoplasmic injection (ICSI) activated oocytes at all pH tested. We suggest that this is due to the pH-sensitivity of the sperm-zona pellucida interaction, which is bypassed during the ICSI procedure. Further development in human embryos is more sensitive to alkalinity than acidity. We discuss these results in terms of the extracellular pH in vivo in the female reproductive tract.

Regulation of intracellular pH during oocyte growth and maturation in mammals

“…The PI mouse embryo has very active HCO K 3 /Cl K exchange for mitigating alkalosis (Baltz et al 1991, Zhao et al 1995, Zhao & Baltz 1996, Phillips & Baltz 1999, which is also seen in human (Dale et al 1998, Phillips et al 2000, hamster (Lane et al 1999a), and, to a lesser extent, bovine embryos (Lane & Bavister 1999). The effectiveness of these exchangers is substantial; one-cell mouse embryos can efficiently progress to blastocyst in conditions of pH w8.2 (normal embryo culture media pH w7.3), provided HCO K 3 /Cl K exchange is functional (Zhao et al 1995).…”

“…A similar lack of HCO K 3 /Cl K exchange activity has been shown in MII hamster oocytes (Lane et al 1999a). The lack of HCO K 3 / Cl K exchange activity in mature unfertilized eggs may not be a property of all mammals, however, as human MII eggs are able to recover from alkalosis, and recovery is inhibited by DIDS (Dale et al 1998, Phillips et al 2000.…”

Effect of embryonic fibroblast cell co-culture on development of mouse embryos following exposure to visible light

“…On the contrary, in vitro produced embryos as well as oocytes are prone to various environmental factors during manipulations in laboratories [1]. The adverse effects of pH fluctuations [2,3], high and low laboratory temperature [4], change in carbon dioxide and O 2 level [5,6] and light [7,8] have been investigated to some extent. Among the environmental factors, light is known to exert some harmful effects on developmental competence of mammalian oocytes and embryos [9].…”

Biological pH buffers in IVF: help or hindrance to success

“…Detailed studies on embryo metabolism, examination of tubal fluid composition and other physiologic, molecular and biochemical insights have led to improved modifications of media formulations. This has resulted in several excellent culture media, both mono and sequential systems, giving laboratories multiple choices in terms of selection of ingredients such as glucose concentration or amino acid complement [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. However, despite the number of options in regard to substrate selection for embryo culture media for use within the laboratory incubator, the ability to select from a variety of pH buffers in handling media for use outside the incubator is extremely limited.…”

“…External pH of culture media (pHe) influences sperm binding and motility [7][8][9], oocyte maturation [10,11] and embryo development [12][13][14][15][16], though confounding factors such as bicarbonate and CO 2 levels exist. Improper intracellular pH (pHi) can impede sperm function [19][20][21][22].…”