title: Concentration dependence of the chloride selfexchange and homoexchange fluxes in human red cell ghosts.
abstract: The concentration dependence of the unidirectional chloride flux in human red cell ghosts was studied under selfexchange and under homoexchange conditions. Under selfexchange conditions the intracellular concentration of chloride [Cl]in is equal to the extracellular concentration [Cl]ex and [Cl]in and [Cl]ex are raised concomitantly. Under homoexchange conditions [Cl]in or [Cl]ex were varied separately at a fixed trans-concentration of chloride. The chloride fluxes were calculated from the rate of the tracer efflux and the intracellular chloride. All experiments were executed in isotonic (330 mosM) KCl/K-citrate/sorbitol solutions containing 0-100 mM KCl, 40 mM K-citrate and different concentrations of sorbitol for isoosmotic substitution. The chloride selfexchange and the chloride homoexchange fluxes exhibit a pure saturation kinetics. The halfsaturation constant for the chloride selfexchange was approximately 20 mM, the maximal flux was approx. 3.5 X 10(-4) mol/(min . g cells). The apparent chloride halfsaturation constants from the homoexchange experiments were in the range of 0.9-4.5 mM for the outer and of 5.5-14.5 mM (0 degree C, pH 7.3) for the inner membrane surface, both halfsaturation constants increase with increasing trans-concentrations. At infinite trans-concentrations of chloride, the halfsaturation constant for the outer and the inner membrane surface amounts to approximately 5 mM and approximately 15 mM, respectively. The slope of the double reciprocal plots of flux versus cis-chloride concentration decreases with increasing trans-concentration of chloride. The kinetics of the chloride transport provides evidence for a carrier mediated transport mechanism with a single reciprocating transport site. The translocation of the loaded carrier appears to be much faster than the translocation of the unloaded carrier.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D002712:Chlorides / Q000378:metabolism*; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006801:Humans; D007474:Ion Exchange; D007700:Kinetics; D009994:Osmolar Concentration
chemical_list: D002712:Chlorides