Abstract
The intracellular volume of neoplastic brain cells was investigated with regard to the effects of hypoโosmolality and hyperosmolality utilizing double isotopic labeling with 3โ0โmethylโDโglucose or tritiated water to measure the total volume of the pellet and inulin or polyethyleneglycol to measure the extracellular volume of the pellet. The cellular pellets were rapidly separated from the incubation medium by centrifugation after addition of an oil mixture. After 60 minutes incubation in Hanks balanced salt medium, the intracellular volume was 7.50 ยฑ 0.64, 8.48 ยฑ 0.19, and 2.97 ยฑ 0.18 ml H~2~O per 10^6^ packed cells for Cโ6 glioma cells, N18TGโ2 neuroblastoma cells, and NG108โ15 neuroblastoma X glioma hybrid cells, respectively. The extracellular trapped space of these cultured cells was about one third of the intracellular volume. The intracellular volume of Cโ6 glioma cells was increased in hypotonic environment, whereas it was decreased with hyperosmolality. Both intracellular sodium and potassium were increased with increased osmolality of the incubation media. These data indicate isoโosmotic regulation by tumor cells, i.e., there is a good correlation between the intracellular volume, intracellular cations and lactate levels of Cโ6 glioma cells under various osmotic conditions.