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Regulation of Intracellular pH in Hamster Preimplantation Embryos by theSodium Hydrogen (Na⁺/H⁺) Antiporter¹

^a Department of Animal Health and Biomedical Sciences, University of Wisconsin, Madison, Wisconsin 53706 ^b Loeb Medical Research Institute and Departments of Obstetrics and Gynecology and Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada K1Y 4E9

This study was an investigation of the mechanisms for the regulation of intracellular pH (pH_i) by hamster preimplantation embryos. The resting pH values of hamster embryos were similar at the 1-cell (7.19 ± 0.34), 2-cell (7.21 ± 0.21), and 8-cell (7.22 ± 0.41) stages. Cleavage-stage hamster embryos alleviated intracellular acidosis by activity of the Na⁺/H⁺ antiporter. The rate of recovery from acidosis was similar for embryos at 1-cell, 2-cell, and 8-cell stages. When Na⁺/H⁺ antiporter activity was inhibited by either incubation in Na⁺-free medium or the presence of an inhibitor, pH_i was unable to recover to initial levels. Instead, pH_i remained acidic. The Na⁺/H⁺ antiporter was also found to contribute to baseline pH regulation, as incubation in Na⁺-free medium resulted in an immediate intracellular acidification. The set point for Na⁺/H⁺ antiporter was pH 7.14. There was no evidence at any developmental stage for activity of either Na⁺-dependent HCO₃^-/Cl^- exchanger or H⁺-ATPase in the regulation of pH_i. Inhibition of the Na⁺/H⁺ antiporter by an amiloride derivative significantly reduced the ability of 2-cell embryos to develop in culture when challenged with acidosis, indicating that the Na⁺/H⁺ antiporter is an essential regulator of pH_i.

¹ This research was supported by National Cooperative Program on Non-Human In Vitro Fertilization and Preimplantation Embryo Development by the National Institute of Child Health and Human Development (NICHD) through Grant HD22023. J.M.B. is a Medical Research Council of Canada Scholar.

² Correspondence: Michelle Lane, Department of Animal Health and Biomedical Sciences, University of Wisconsin, 1655 Linden Drive, Madison, WI 53706. FAX: 608 262 7420; lane{at}ahabs.wisc.edu

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