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.

Cell volume regulation in mammalian oocytes and preimplantation embryos

“…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). It had not yet been established that these exchangers can also function in cell volume regulation in preimplantation embryos.…”

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).…”

“…Oddly, NHE activity in mouse embryos varies widely among mouse strains, and in at least some strains it is not robust (Steeves et al 2001). As is the case for HCO K 3 /Cl K exchanger activity, NHE activity is present in the PI embryos of human (Phillips et al 2000), hamster (Lane et al 1998), and bovine (Lane & Bavister 1999), and inhibition impairs PI development (Lane et al 1998). In addition, early embryos possess monocarboxylate transporters that cotransport H C and can influence pH i of the embryo (Harding et al 1999), although this is not pH regulation per se, but a manifestation of passive transport of H C as lactic acid across the plasma membrane.…”

Phospho-Signaling at Oocyte Maturation and Fertilization: Set Up for Embryogenesis and Beyond Part II. Kinase Regulators and Substrates

“…The function of Na + /H + exchanger has also been described even for later stage of development e.g. blastocyst of mouse (Barr et al 1998), bovine embryos (Lane and Bavister 1999) and human pre-implantation embryos (Phillips et al 2000).…”