Chloride permeability in human red cells: Influence of membrane protein rearrangement resulting from ATP depletion and calcium accumulation

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Abstract
As 15% of band 3 protein, the assumed chloride channel, is associated with spectrin, the major peripheral protein of a lattice located at the red cell membrane-cytosol interface, the present study was undertaken to evaluate whether a rearrangement of the lattice modifies the functional property of band 3 protein. Such a rearrangement was modulated by depletion of cell ATP and/or by accumulation of Ca2+ ions within the cell. ATP depletion induces an inhibition of the electroneutral one-for-one chloride exchanges. Neither the modification of red cell morphology due to ATP depletion (discocyte-echinocyte transformation) nor a direct effect of the decrease in internal ATP level can account for this inhibition. On the other hand, it seems reasonable to consider that inhibition is related to the changes in membrane protein organization (formation of heteropolymers) induced by the decrease in ATP level. But it does not appear that the degree of inhibition is modified when this altered assembly of membrane protein is stabilized by disulfide linkages. Accumulation of Ca2+ ions in the cell at a relatively low concentration (10μm range) inhibits chloride exchange without apparent modification of the assembly of membrane proteins. This effect of calcium on chloride exchanges is speculatively denoted as a “direct” effect of calcium. Calcium loading of fresh red cells at higher concentrations (500 to 1000 μm) obtained by use of the ionophore A23187 induces a very strong inhibition of chloride exchanges. In this case, inhibition can be reasonably accounted for by two simultaneous effects of calcium: a “direct” effect which explains half of the inhibition and an “indirect” effect due to the formation of membrane protein complexes stabilized by covalent crosslinkages (activation by Ca2+ ions of a transglutaminase). It is interesting to note that intracellular calcium, whatever the level, inhibits electroneutral exchanges of chloride but increases net chloride movements.