Effects of halides and bicarbonate on chloride transport in human red blood cells.

Abstract

Chloride self-exchange was determined by measuring the rate of 36Cl efflux from human red blood cells at pH 7.2 (0.degree. C) in the presence of fluoride, bromide, iodide and bicarbonate. The chloride concentration varied between 10-400 mM and the concentration of other halides and bicarbonate between 10-300 mM. Chloride equilibrium flux showed saturation kinetics. The half-saturation constant increased and the maximum flux decreased in the presence of halides and bicarbonate; the inhibition kinetics were both competitive and noncompetitive. The competitive and the noncompetitive effects increased proportionately in the sequence: fluoride < bromide < iodide. The inhibitory action of bicarbonate was predominantly competitive. The noncompetitive effect of chloride (chloride self-inhibition) on chloride transport was less dominant at high inhibitor concentrations. Similarly, the noncompetitive action of the inhibitors was less dominant at high chloride concentrations. The results can be described by a carrier model with 2 anion binding sites: a transport site and a second site which modifies the maximum transport rate. Binding to both types of sites increased proportionately in the sequence: fluoride < chloride < bromide < iodide.