Differences in Intracellular pH Regulation by Na+/H+ Antiporter among Two-Cell Mouse Embryos Derived from Females of Different Strains1

Regulation of intracellular pH (pH(i)) by two-cell-stage embryos derived from female mice of three different strains (CF-1, Balb/c, and BDF) was investigated. Embryos recovered at a slow rate from intracellular acidosis produced by a pulse of NH(4)Cl; the rate did not differ significantly among strains. Recovery was reversibly inhibited by amiloride or the absence of Na(+), implicating Na(+)/H(+) antiporter activity. The threshold pH(i) (setpoint) below which Na(+)/H(+) antiporter activity was elicited was approximately 7.15 for each strain. No recovery from induced acidosis occurred in the absence of external Na(+) in any strain, and thus embryos could be maintained in acidosis for an extended period. Upon reintroduction of Na(+), embryos derived from either CF-1 or BDF females recovered at a slow rate comparable to that measured in embryos not maintained for a period in Na(+)-free medium, but embryos derived from Balb/c females consistently recovered at a highly accelerated rate. This accelerated recovery appeared to be due, in part, to an activation of the Na(+)/H(+) antiporter in Balb/c-derived embryos, which did not occur in CF-1- or BDF-derived embryos. Thus, embryos derived from different strains of female mice differ in their control of mechanisms for pH(i) regulation.