APPARENT ABSENCE OF NA+-H+ ANTIPORT ACTIVITY IN THE 2-CELL MOUSE EMBRYO

We have used the pH-sensitive dye BCECF to investigate the regulation of intracellular pH (pHi) by two-cell stage mouse embryos in bicarbonate-free medium. There is no indication of a Na+ H+ antiport active in regulating pHi, as recovery from acid-loading was insensitive to amiloride, ethylisopropylamiloride, or the absence of extracellular Na+. Instead, protons appear to be in equilibrium across the plasma membrane, as indicated by the response of pHi to changes in external K+. The embryos have an intracellular buffering power in the normal range (25.3 mM/pH); their apparent permeability to protons is, however, very high (0.22 cm/sec). © 1990.