The role pf sodium and potassium in regulating amino acid accumulation and protein synthesis in LM-strain mouse fibroblasts

Abstract

The effect of varying the Na + to K + ratio has been studied in relation to the regulation of amino 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 NcCl and KCl. 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: 1. 1. 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. 2. 2. The ony requirements for the uptake and accumulation of L-leucine and Lglutamin acid into LM cells is the simultaneous presence of Na + and K + in the extracellular acqueous phase. The quantity accumulated is dependent upon the ration 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. 3. 3. The quantity of L-leucine accumulated by LM cells is also determined by the extracellular concentration of the amino acid at all of the Na + to K + ratios studied. The extent of concentration over the extracellular level is always greatest at the lowest external levels. 4. 4. Other ingredients in a standard tissue-culture medium such as Ca 2+, Mg 2+, glucose, vitamins and serum do not affect tha accumulation of L-leucine. However, other amino acids suppress the accumulation of L-leucine. 5. 5. The extent of amino acid incorporated into cellular proteins is directly related to the intracellular level of that amino acid. 6. 6. The growth of LM cell populations can be controlled in synthetic media by varrying the concentration ratio of Na + to K +.