The effect of ATP, intracellular calcium and the anion exchange inhibitor DIDS on conductive anion fluxes across the human red cell membrane

Abstract

The influence of ATP depletion, the intracellular ionized Ca-concentration, anion substitution and DIDS on the conductive anion fluxes across the human red cell membrane has been examined. Under physiological or near physiological conditions it is not possible to observe conductive anion fluxes across the erythrocyte membrane in that anions totally dominate the membrane conductance. Consequently anions are at electrochemical equilibrium and the netflux is zero. However, conductive anion fluxes can be induced by raising the potassium conductance, either by addition of valinomycin, or by triggering the native calcium activated potassium channel by addition of the Ca 2+ ionophore A23187 to cells suspended in a calcium containing medium. The interpretation of data from experiments with valinomycin induced netfluxes has normally been done according to a constant field model, and the results have consequently been given as permeabilities. Since it has been demonstrated recently, that these cation pathways do not conform to a constant field scheme (Bennekou, P. and Christophersen, P. (1986) J. Membr. Biol. 93, 221–227 and Vestergaard-Bogind, B., Stampe, P. and Christophersen, P. (1985) J. Membr. Biol. 88, 67–75), it has been chosen, instead of permeabilities, to calculate the ion conductance from net efflux data, using an independent estimate of the membrane potential. The main result reported, is that only one component is found for the conductive anion fluxes in the presence of DIDS using the latter theoretical framework, whereas a sizeable DIDS-insensitive component is found when the constant field analysis is used. Furthermore it is found that ATP and intracellular calcium do not influence the anion conductances.