title: Effect of extracellular potassium on amino acid transport and membrane potential in fetal human fibroblasts.
abstract: The distribution ratio of the lipophilic cation tetraphenylphosphonium (TPP+) has been used to estimate the electrical potential difference across the plasma membrane in cultured human fibroblasts. These cells exhibit a membrane potential markedly influenced by the diffusion potential of K+. High extracellular potassium concentrations depolarize human fibroblasts and depress the activity of transport systems A, ASC (both serving for zwitterionic amino acids), X-AG (for anionic amino acids), and y+ (for cationic amino acids). High doses (100 microM) of the K+-ionophore valinomycin hyperpolarize the cells. This condition enhances the activity of systems A, ASC and y+. Transport systems L (for neutral amino acids) and x-C (for anionic amino acids) are insensitive to changes in extracellular K+ or to valinomycin. System X-AG is inhibited by the addition of 100 microM valinomycin, but the effect of the ionophore appears to be potential-independent. These results indicate that: (a) the activity of systems L and x-C is potential-independent and (b) the activity of systems A, ASC, X-AG and y+ is sensitive to alterations of external [K+] associated to changes in membrane potential.
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000621:Aminoisobutyric Acids / Q000378:metabolism; D001224:Aspartic Acid / Q000378:metabolism; D001693:Biological Transport, Active; D001834:Body Water; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D009861:Onium Compounds / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology*; D011247:Pregnancy; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D000621:Aminoisobutyric Acids; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D014634:Valinomycin; C017911:2-(methylamino)isobutyric acid; D001224:Aspartic Acid; D011188:Potassium; C013289:tetraphenylphosphonium