ROLE OF SODIUM AND POTASSIUM IN REGULATING AMINO ACID ACCUMULATION AND PROTEIN SYNTHESIS LM-STRAIN MOUSE FIBROBLASTS

The effect of varying the Na+ to K+ ratio has been studied in relation to the regulation of amlno acid accumulation, protein synthesis and cell growth in LM-strain mouse fibroblasts. Amino acid accumulation and protein synthesis in these cells was first observed In simple salt solutions containing only Nad and KC1. Other essential ingredients for LM cell growth were sequentially tested for their effect in addition to Na+ and K+. Later, cell growth was followed in synthetic media in which only the Na+ to K+ ratio varied. The following have been noted: The external Na+ to K+ ratio determines the volume of LM cells. The volume Increases as the K+ to Na* ratio is raised. The increased cell volume is directly related to an increased intracellular K+ level; The only requirements for the uptake and accumulation of L-leucine and L-glutamic acid into LM cells is the simultaneous presence of Na+ and K+ In the extracellular aqueous phase. The quantity accumulated is dependent upon the ratio of Na+ to K+. A maximum intracellular level for both amino acids occurs when the ratio of Na+ to K+ is approx. 140:10 mequiv/L; The quantity of L-leucine accumulated by LM cells is also determined by the extracellular concentration of the amlno acid at all of the Na+ to K+ ratios studies. The extent of concentration over the extracellular level Is always greatest at the lowest external level; Other ingredients in a standard tissue-culture medium such as Ca2+ , Mg^+, glucose, vitamins and serum do not affect the accumulation of L-leucine. However, other amino acids suppress the accumulation of L-leucine; The extent of amlno acid incorporated into cellular proteins is directly related to the intracellular level of that amino acid; The growth of LM cell populations can be controlled In synthetic media by varying the concentration ratio of Na+ to K+.