title: Intracellular pH regulation in human preimplantation embryos.
abstract: We report here that intracellular pH (pH(i)) in cleavage-stage human embryos (2-8-cell) is regulated by at least two mechanisms: the HCO(3)(-)/Cl(-) exchanger (relieves alkalosis) and the Na(+)/H(+) antiporter (relieves acidosis). The mean pH(i) 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 HCO(3)(-)/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 HCO(3)(-)/Cl(-) exchanger was between pH(i) 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 pH(i) 6.8; this recovery was HCO(3)(-)-independent and amiloride-sensitive, with a pH(i) set-point of approximately 6.8-6.9. A second system that was both Na(+)- and HCO(3)(-)-dependent appeared to mediate further recovery from acidosis up to about pH(i) 7.1. Thus, pH(i) of early human preimplantation embryos appears to be regulated by opposing mechanisms (HCO(3)(-)/Cl(-) exchanger, Na(+)/H(+) antiporter, and possibly a third acid-alleviating transporter that was both Na(+)- and HCO(3)(-)-dependent) resulting in the maintenance of pH(i) within a narrow range.
authors.affiliation: Loeb Research Institute, Ottawa Hospital and Department Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: K P
authors.initials: KP
authors.lastname: Phillips
authors.forename: M C
authors.initials: MC
authors.lastname: Léveillé
authors.forename: P
authors.initials: P
authors.lastname: Claman
authors.forename: J M
authors.initials: JM
authors.lastname: Baltz
mesh_terms: D000136:Acid-Base Equilibrium; D000138:Acidosis; D000471:Alkalosis; D017920:Antiporters / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism; D004622:Embryo, Mammalian / Q000502:physiology*; D047108:Embryonic Development; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009865:Oocytes / Q000502:physiology; D011247:Pregnancy
chemical_list: D017920:Antiporters; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides