Bicarbonate/chloride exchange and intracellular pH throughout preimplantation mouse embryo development

Abstract

HCO3-/Cl- exchanger activity, which regulates intracellular pH (pHi) in the alkaline range, has been shown to be present throughout preimplantation mouse embryo development and to be necessary for embryo viability. We have characterized HCO3-/Cl- exchange activity and its regulation of pHi throughout preimplantation development (1-cell, 2-cell, morula, and blastocyst stages). Embryos at each stage can recover from alkalosis. Recovery was dependent on external [Cl-], activated by increased pHi, and inhibited by the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and external HCO3-. Dependence of exchanger activity on external [Cl-] and pHi remained unchanged during preimplantation development. However, the concentration at which DIDS inhibits the maximal response by 50% increased significantly (by approximately 5-fold) after the one-cell stage. In addition, HCO3-/Cl- exchange activity decreased over the course of development, with significantly lower activity at the morula and blastocyst stages relative to the one- and two-cell stages, coinciding with the movement of embryo from the high pH environment of the oviduct to the lower pH environment of the uterus.

CFTR mediates bicarbonate-dependent activation of miR-125b in preimplantation embryo development

“…The expression levels of miR-125b in two-cell and four-cell embryos were significantly higher than that in morula and blastocyst stage (Figure 2A), which coincides with the transit of embryo from oviduct (high bicarbonate concentration) to the uterus (lower bicarbonate concentration) [42]. This suggested that the window for HCO 3 − -dependent miR-125b activation occurs from fertilization to four-cell stage but not in subsequent stages.…”

Cell volume regulation in mammalian oocytes and preimplantation embryos

“…Baltz, unpublished). Similarly, HCO 3 À /Cl À exchange can be activated by alkalosis throughout preimplantation mouse embryo development (Baltz et al, 1991;Zhao et al, 1995;Zhao and Baltz, 1996;Cetinkaya and Erdogan, 2008), principally mediated by AE2 (Phillips and Baltz, 1999;Zhou et al, 2009). Similar findings have been reported for preimplantation embryos of human (Phillips et al, 2000), hamster (Lane et al, 1998(Lane et al, , 1999a, and bovine (Lane and Bavister, 1999).…”

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].…”

“…Improper intracellular pH (pHi) can impede sperm function [19][20][21][22]. Improper pHi is also detrimental to embryo development [23][24][25][26][27], impairs embryo metabolism [28,29], alters organelle localization [30], and even retards resulting fetal growth [31]. Furthermore, periodic fluctuations in environmental conditions, such as the pHe of media, can be harmful as these can be transduced into deleterious intracellular perturbations [32].…”