Time-dependence of, and effects of inhibition and cellular aging on, chloride efflux across erythrocyte membranes in Huntington's disease

Previous studies have demonstrated an increased rate of chloride transport across erythrocyte membranes in Huntington's disease, a process regulated at the external side of the major transmembrane protein Band 3. A marked effect of time was noted in 3 Huntington's disease samples that were studied more than 4 h after obtaining the blood. In order to study anion transport more closely in Huntington's disease and the apparent time-dependence of chloride efflux in this disorder, we have performed several sets of experiments. Chloride transport in Huntington's disease erythrocytes was found to be extremely sensitive to time with the efflux rate constant decreasing by approximately 30% over a 24 h period. Chloride transport in control cells was unaffected by time. Inhibition studies with the specific anion transport blocker 4,4′-diisothiocyanto-2,2′-disulfonic acid stilbene (DIDS) demonstrated that the same degree of inhibition of chloride transport could be achieved at a much lower concentration of DIDS in Huntington's disease than in controls. Comparison of chloride efflux in fractions enriched in young and old erythrocytes, respectively, obtained by density centrifugation of fresh blood, demonstrated that only in the young fraction of cells was chloride efflux diminished with time in Huntington's disease. Chloride transport in in vivo aged Huntington's cells or both young and old control cells was essentially not dependent on time. These results are discussed in terms of proposed molecular mechanisms for neuronal loss in this disorder. The alterations in chloride efflux in extraneural erythrocytes are consistent with a proposed cell-surface membrane defect involving a protein in Huntington's disease.