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Human Reproduction, Vol. 15, No. 4, 896-904, April 2000
© 2000 European Society of Human Reproduction and Embryology

Intracellular pH regulation in human preimplantation embryos

Karen P. Phillips1,3, Marie-Claude Léveillé2,4, Paul Claman2,4 and Jay M. Baltz1,2,3,4,5

1 Loeb Research Institute, Ottawa Hospital and Departments of 2 Obstetrics and Gynecology, (Division of Reproductive Medicine), 3 Cellular and Molecular Medicine, University of Ottawa and 4 Human IVF Program, Ottawa Hospital, Ottawa, Ontario,Canada K1Y 4E9

We report here that intracellular pH (pHi) in cleavage-stage human embryos (2–8-cell) is regulated by at least two mechanisms: the HCO3–/Cl– exchanger (relieves alkalosis) and the Na+/H+ antiporter (relieves acidosis). The mean pHi of cleavage-stage embryos was 7.12 ± 0.008 (n = 199) with little variation between different stages. Embryos demonstrated robust recovery from alkalosis that was appropriately Cl–-dependent, indicating the presence of the HCO3–/Cl– exchanger. This was further confirmed by measuring the rate of intracellular alkalinization upon Cl– removal, which was markedly inhibited by the anion transport inhibitor, 4,4'-diisocyanatostilbene-2,2'-disulphonic acid, disodium salt. The set-point of the HCO3–/Cl– exchanger was between pHi 7.2 and 7.3. Embryos also exhibited Na+-dependent recovery from intracellular acidosis. Na+/H+ antiporter activity appeared to regulate recovery up to about pHi 6.8; this recovery was HCO3–-independent and amiloride-sensitive, with a pHi set-point of ~6.8–6.9. A second system that was both Na+- and HCO3–-dependent appeared to mediate further recovery from acidosis up to about pHi 7.1. Thus, pHi of early human preimplantation embryos appears to be regulated by opposing mechanisms (HCO3–/Cl– exchanger, Na+/H+ antiporter, and possibly a third acid-alleviating transporter that was both Na+- and HCO3–-dependent) resulting in the maintenance of pHi within a narrow range.

Key words: embryo/HCO3–/Cl– exchanger/Na+/H+ antiporter/pH

5 To whom correspondence should be addressed at: Loeb Research Institute, Ottawa Hospital, Civic Site, 725 Parkdale Ave, Ottawa, Ontario K1Y 4E9, Canada


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