Regulation of intracellular pH in bovine oocytes and cleavage stage embryos

This study investigated the mechanisms for the regulation of intracellular pH in bovine oocytes and embryos. Na(+)/H(+) antiporter activity for the regulation of intracellular pH in the acid to neutral range was detected in both in vitro matured bovine oocytes and in vitro produced embryos. However, the activity of the antiporter was significantly reduced in oocytes compared to 2-cell, 4-cell, and 8-cell embryos. HCO(3)(-)/Cl(-) exchanger activity could be detected in oocytes and embryos using the chloride removal method, however the ability of this transporter to regulate intracellular pH against an alkaline load was poor and intracellular pH could not be re-established. The inability of the HCO(3)(-)/Cl(-) exchanger to adequately regulate intracellular pH was further highlighted by the arrest of embryos at the 8-16 cell stage when challenged with a small alkaline load. Therefore, bovine embryos are extremely sensitive to alterations in intracellular pH above the resting value of around 7.2. This sensitivity could account in part for impaired development and viability of bovine embryos produced in vitro.