Factors affecting the relative magnitudes of the ouabain-sensitive and the ouabain-insensitive fluxes of thallium ion in erythrocytes.
A maximal rate of the ouabain-sensitive 204-Tl influx in human erythrocytes can be attained at trace concentrations of Tl+ in Mg2+ isotonic media free of K+ and Na+. The maximal influx of Tl+ from isotonic Mg(NO3)2 at 20 degrees C and pH 7.4 was 0.45 mM.l(-1).h-1 with a Km of 0.025 mM. In contrast to the active influx of Tl+, the passive Tl+ fluxes were neither saturated nor influenced by external cations in the range of concentrations of Tl+ and K+ studied. The rate constants of Tl+ passive fluxes in human and cat erythrocytes can be related to pH by the equation log kin(OUT)= -A + B.pH, where A and B are empirical constants for particular conditions. The apparent activation energy was 16 and 11 kcal/mol in sulphate and nitrate media, respectively. Tl+ and the alkali metal cations seem to overcome a common barrier in the erythrocyte membrane. Nevertheless, the rate of the passive penetration of Tl+ is about two orders of magnitude faster than those of K+ or Rb+. An extra non-Coulombic interaction between Tl+ and membrane ligands appears to be involved providing an accumulation of Tl+ somewhere in the vicinity of the membrane barrier and increasing the diffusion fluxes of Tl+ in both directions.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001693:Biological Transport, Active / Q000187:drug effects; D002415:Cats; D002463:Cell Membrane Permeability; D004910:Erythrocyte Membrane / Q000502:physiology; D004912:Erythrocytes / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D010042:Ouabain / Q000494:pharmacology*; D012413:Rubidium / Q000378:metabolism; D013045:Species Specificity; D013793:Thallium / Q000378:metabolism*
D010042:Ouabain; D013793:Thallium; D012413:Rubidium