A sodium ion concentration gradient formed during the absorption of glycine by mouse ascites-tumour cells.

1. To deplete them of ATP the tumour cells were starved at 37 degrees in a Ringer solution containing 33m-equiv. of Na(+)/l., 131m-equiv. of Li(+)/l., 2mM-sodium cyanide and 0.1mm-ouabain. The cellular content of K(+) was largely replaced by Li(+), but cellular [Na(+)] remained near 33m-equiv./l. 2. The addition of 12mm-glycine to the system caused cellular [Na(+)] to increase, during the next 4min., by about 4m-equiv./l., so that it slightly exceeded extracellular [Na(+)]. This occurred in parallel with the absorption of glycine. 3. The cellular K(+) content fell by an amount representing about 10% of the amount of Na(+) absorbed. 4. The results provide a clear demonstration that the flow of glycine into the cells is linked to a parallel movement of Na(+); K(+) appears to play a facultative role in the carrier system, whereas Li(+) is almost inert. 5. The effects produced by glycine were not reproduced by l-arabinose.