Sodium concentrations affect metabolite uptake and cellular metabolism

Abstract

Rates of uptake of glucose (measured with ³H‐2‐deoxy‐d‐glucose), galactose, and leucine increase after exposure of chick embryo cells to increasing concentrations of Na⁺ over the range 100 to 200 mM. Uptake of nucleosides was unaffected by [Na⁺] over this range. Prior exposure of cells was required for the [Na⁺] effect on uptake. Changes were measureable within two hours after changing [Na⁺], and although the capacity for deoxyglucose uptake remained constant thereafter, the capacity for leucine uptake continued to change during the next few hours. Inhibition of protein synthesis by cycloheximide, or of RNA synthesis by Actinomycin D, failed to prevent these uptake changes. Analysis of the kinetics of uptake showed that only the Km for uptake of deoxyglucose or leucine was affected by [Na⁺]; the maximum V for each compound remained the same. Effects of [Na⁺] could be distinguished from the increased capacity for glucose uptake induced by glucose starvation. Incorporation of both radioactive uridine into RNA, and radioactive thymidine into DNA, were affected by [Na⁺], but the differences were not correlated with uptake of other metabolites. No differences in countable mitoses were apparent, although the growth of chick embryo cells increased slightly with increasing [Na⁺]. Changes in uptake due to differing [Na⁺] also were observed in mammalian (rat NRK) cells. However, no effects of [Na⁺] on rates of cell growth or saturation density were observed with these cells.