Na+/H+ antiporter activity in hamster embryos is activated during fertilization

This study characterized the activation of the regulatory activity of the Na+/H+ antiporter during fertilization of hamster embryos. Hamster oocytes appeared to lack any mechanism for the regulation of intracellular pH in the acid range. Similarly, no Na+/H+ antiporter activity could be detected in embryos that were collected from the reproductive tract between 1 and 5 h post-egg activation (PEA). Activity of the Na+/H+ antiporter was first detected in embryos collected at 5.5 h PEA and gradually increased to reach maximal activity in embryos collected at 7 h PEA. Parthenogenetically activated one-cell and two-cell embryos demonstrate Na+/H+ antiporter activity, indicating that antiporter activity is maternally derived and initiated by activation of the egg. The inability of cycloheximide, colchicine, or cytochalasin D to affect initiation of antiporter activity indicates that antiporter appearance is not dependent on the synthesis of new protein or recruitment of existing protein to the cell membrane. In contrast, incubation of one-cell embryos with sphingosine did inhibit the appearance of Na+/H+ antiporter activity, showing that inhibition of normal protein kinase C activity is detrimental to antiporter function. Furthermore, incubation of oocytes with a phorbol ester which stimulates protein kinase C activity induced Na+/H+ antiporter activity in oocytes in which the activity was previously absent. Incubation with an intracellular calcium chelator also reduced the appearance of antiporter activity. Taken together, these data indicate that the appearance of Na+/H+ antiporter activity following egg activation may be due, at least in part, to regulation by protein kinase C and intracellular calcium levels.