Cryopreservation reduces the ability of hamster 2-cell embryos to regulate intracellular pH

Vitrification of hamster 2-cell embryos impairs the activity of both the Na+/H+ antiporter and HCO3-/Cl- exchanger; the two transport proteins responsible for the regulation of intracellular pH (pHi). The activities of both the Na+/H+ antiporter and HCO3-/Cl- exchanger were significantly reduced at 4 h following warming compared to freshly collected embryos. Normal levels of activity of both transporters were not restored until 6 h after warming. Thus, cryopreservation of cleavage stage hamster embryos has a detrimental effect on their ability to maintain intracellular ionic homeostasis. Impairment of these pHi regulatory proteins resulted in the pHi of embryos being significantly elevated from the control values of 1.2 to 7.35 for approximately 4 h after warming. In addition, an elevated pHi value significantly impaired oxidative metabolism. Therefore, the loss in developmental competence of embryos following cryopreservation mag in part be explained by a reduced ability to regulate intracellular pH that results in perturbations in metabolism and disruption of energy production.