1. The tumour cells were starved in a solution lacking Na+ and then transferred to a Ringer solution containing 2mm-sodium cyanide, 150m-equiv. of Na+/l. and 10m-equiv. of K+/l. Such cells were depleted of ATP and contained an endogenous pool of various amino acids equivalent to a 26mm solution. 2. At 4min. after the transfer the cellular Na+ content had increased by about 100% and roughly an equivalent amount of K+ had left the cells. 3. Under these conditions [14C]glycine was absorbed from an 11mm solution and reached the same cellular concentration by about 4min. The pool size increased by approximately the same amount (ΔGly), so glycine did not simply exchange with the endogenous components. 4. After 4min. with glycine, the cells contained about 20% more Na+ (ΔNa+) than the control and about 10% less K+ (ΔK+). The mean values of ΔNa+/ΔGly and ΔK+/ΔGly from five experiments were respectively 0·90±0·11 and 0·62±0·11equiv./mole. 5. A further indication that these two ratios were not equal was that the cells absorbed more water than the movement of glycine itself required. The excess of water was osmotically equivalent to 0·95±0·16equiv. of solute/mole of glycine absorbed. 6. The variation of ΔNa+/ΔGly with the duration of the incubation was consistent with the stimulated uptake of Na+ being linked to the actual transport of glycine. The same may apply to the movement of K+, though the time-dependence was not examined in that case. 7. The observations were analysed in terms of a model in which both K+ and Na+ moved with a glycine-carrier system without ATP being involved. The analysis supported the idea that the spontaneous movements of the ions through the system might concentrate glycine in the cells significantly by purely physical means (Christensen's hypothesis).

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