oxonol-v and Carcinoma--Ehrlich-Tumor

Studies with membrane vesicles and with whole cell preparations have shown clearly that the electrochemical gradient of Na+ acting across the cell membrane is closely coupled to the influx and efflux of amino acids or carbohydrates through their cellular pumps. It has been less clear (1) just how tightly solute flow is coupled to that of Na+ in stoichiometrical terms and (2) whether coupling is tight enough to account for the maximum solute gradients that the systems form in vivo. Recent work with ionophores, including nigericin, has revealed circumstances in preparations of mouse ascites-tumor cells where if the sodium gradient hypothesis is correct, electrogenic ion pumping must be supposed to maintain membrane potentials of the order of 80 mV negative. We have used a new fluorescence assay based on an oxonol dye in a search for potentials of that magnitude. Their possible origin is discussed.

Topics: Adenosine Triphosphate; Amino Acids; Animals; Biological Transport, Active; Carcinoma, Ehrlich Tumor; Carrier Proteins; Cell Membrane; Electrochemistry; Energy Metabolism; Fluorescent Dyes; Humans; Indicators and Reagents; Ion Channels; Ionophores; Isoxazoles; Kinetics; Membrane Potentials; Mice; Models, Biological; Nigericin; Sodium

The plasma membrane potential of Lettré cells has been determined with the optical indicator oxonol-V and found to be -57 mV at 37 degrees C (range -20 to -80 mV depending on the physiological condition of the cells). Increasing extracellular K+ does not depolarize cells: even in the presence of 155 mM K+ the potential is -41 mV; membrane potential is also insensitive to the chemical gradient of Na+, Mg2+, Ca2+ or Cl-. Ouabain depolarizes the cells; H+ efflux from cells is stimulated by extracellular Na+. We propose that in Lettré cells the plasma membrane potential is generated by electrogenic cation pumps. The balancing fluxes of Na+ and K+ are mainly through electroneutral cation exchanges (Na+/K+ and Na+/H+) and the magnitude of the potential is limited by organic anion leaks. Such a mechanism may operate in other biological membranes also.

Topics: Animals; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; Carcinoma, Ehrlich Tumor; Cations; Cell Membrane; Fluorescent Dyes; Isoxazoles; Kinetics; Membrane Potentials; Mice; Models, Biological; Ouabain; Thermodynamics; Valinomycin