Effects of medium amino acids on ouabain-sensitive 86Rb+ -uptake and membrane-potential dependent [3H]tetraphenylphosphonium accumulation in Friend erythroleukemia cells.
The effects of amino acids present in minimal essential medium were investigated on 86Rb+ -fluxes and on the membrane-potential dependent accumulation of the lipophilic cation [3H]tetraphenylphosphonium (TTP+) in logarithmically growing Friend erythroleukemia cells. The ouabain-sensitive 86Rb+ -uptake measured as well in complete growth medium as in Earle's balanced salt solution (EBSS) with amino acid composition present in growth medium, was 3 to 4-fold increased in comparison to the 86Rb+-uptake measured in pure EBSS only. The Na+,K+,2Cl- -cotransport measured as piretanide-sensitive 86Rb+-uptake was reduced in the presence of amino acids. Stimulation of the ouabain-sensitive 86Rb+ -uptake could be brought about by the addition of alanine alone or of the sodium ionophore monensin. In spite of the activation of the Na+,K+ -pump the membrane-potential dependent accumulation of [3H]TPP+ was about 40 per cent reduced in the presence of medium amino acids indicating a decreased membrane potential under these conditions. On the other hand, monensin which induces an electrically silent Na+ -influx via Na+/H+ -exchange was shown to hyperpolarize the membrane on the basis of [3H]TPP+-accumulation. These results suggest that the intensive uptake of neutral amino acids by Na+-cotransport in rapidly growing cells may be responsible for both stimulation of the Na+,K+ -pump and decrease in the transmembrane potential.
Schaefer
A
A
Abteilung für Allgemeine Toxikologie, Universität Hamburg/Bundesrepublik Deutschland.
Munter
K H
KH
Rüller
S
S
D000596:Amino Acids / Q000494:pharmacology*; D002460:Cell Line; D003470:Culture Media / Q000494:pharmacology; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute; D008564:Membrane Potentials / Q000187:drug effects; D008985:Monensin / Q000494:pharmacology; D009861:Onium Compounds / Q000493:pharmacokinetics*; D009943:Organophosphorus Compounds / Q000493:pharmacokinetics*; D010042:Ouabain / Q000494:pharmacology*; D012414:Rubidium Radioisotopes / Q000493:pharmacokinetics*; D014407:Tumor Cells, Cultured / Q000378:metabolism* / Q000502:physiology
D000596:Amino Acids; D003470:Culture Media; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D012414:Rubidium Radioisotopes; D010042:Ouabain; D008985:Monensin; C013289:tetraphenylphosphonium