Differential effects of transmembrane potential on two Na+-dependent transport systems for neutral amino acids.
The effects of changes of membrane potential on amino acid transport through systems A, ASC and L was investigated in the Ehrlich cell and the human erythrocyte. Changes of membrane potential were produced by incubating cells whose K+ permeability had been increased, either by valinomycin or by activation of Ca2+-dependent K+ channels, in medium containing different K+ concentrations. The changes in membrane potential were followed by measuring the distribution ratio reached by lipophilic indicators. Transport through Na+-dependent system A was sensitive to the membrane potential, the rate of amino acid uptake increasing 2.2-3.1-times for each 60 mV-hyperpolarization. The Na+-dependent system ASC was insensitive to membrane potential. The Na+-independent system L was not directly affected by membrane potential, but the steady-state accumulation of system L substrates was increased by hyperpolarization.
M
M
Valdeolmillos
J
J
García-Sancho
B
B
Herreros
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000596:Amino Acids / Q000378:metabolism*; D000598:Amino Acids, Cyclic; D000818:Animals; D001693:Biological Transport, Active; D002286:Carcinoma, Ehrlich Tumor; D004910:Erythrocyte Membrane; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials; D051379:Mice; D009861:Onium Compounds / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D012964:Sodium / Q000502:physiology*; D014320:Triphenylmethyl Compounds / Q000494:pharmacology
D000596:Amino Acids; D000598:Amino Acids, Cyclic; D009861:Onium Compounds; D014320:Triphenylmethyl Compounds; C011561:triphenylmethylphosphonium; C006504:2-aminobicyclo(2,2,1)heptane-2-carboxylic acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D012964:Sodium; D011433:Propranolol; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium