Expression and function of bicarbonate/chloride exchangers in the preimplantation mouse embryo

Bicarbonate/chloride (HCO3-/Cl-) exchangers regulate intracellular pH in the alkaline range. Previously, it has been shown that mouse embryos at the two-cell stage exhibit this activity, but that the otherwise ubiquitous mechanisms for regulating intracellular pH in the acid-to-neutral range are undetectable. We have examined mouse embryos during preimplantation development (one-cell zygote through blastocyst) to determine whether HCO3-/Cl- exchange activity exists at all stages, whether it is necessary for preimplantation development, and whether messenger RNAs from the known HCO3-/Cl- exchanger genes are expressed. We have found that all stages of preimplantation embryo have detectable HCO3-/Cl- exchange activity. In addition, inhibition of this activity with the stilbene anion exchange inhibitor DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid) disrupts intracellular pH homeostasis and markedly inhibits embryo development from the two-cell stage to blastocysts in culture under conditions of moderately high external pH. Finally, mRNA encoding two members of the band 3-related AE anion exchanger gene family are expressed in preimplantation embryos.