Low Na+ concentration: a factor contributing to diminished uptake and incorporation of amino acids by diapausing mouse blastocysts?

Uptake and incorporation of 14C amino acids by normal and diapausing blastocysts was found to be Na+ dependent with one exception. Delayed embryos preincubated 25 h in medium containing 124 mM Na+ had labeling characteristics independent of the Na+ concentration present during labeling. Since diapausing embryos preincubated 25 h in low Na+ medium (55mM) retained their Na+ dependent labeling characteristics, delayed blastocysts may be in a low Na+ environment in situ. Low Na+ may explain why delayed blastocysts are unable to utilize radioactive methionine in vivo (Weitlauf and Greenwald, '68).