Anion Exchanger 1 or Band 3 is a membrane protein responsible for the rapid exchange of chloride for bicarbonate across the red blood cell membrane. Nine mutations leading to single amino-acid substitutions in the transmembrane domain of AE1 are associated with dominant hereditary stomatocytosis, monovalent cation leaks and reduced anion exchange activity. We set up a stopped-flow spectrofluorometry assay coupled with flow cytometry to investigate the anion transport and membrane expression characteristics of wild-type recombinant AE1 in HEK293 cells, using an inducible expression system. Likewise, study of three stomatocytosis associated mutations (R730C, E758K and G796R), allowed the validation of our method. Measurement of the rapid and specific chloride/bicarbonate exchange by surface expressed AE1 showed that E758K mutant was fully active compared to WT AE1, whereas R730C and G796R mutants were inactive, reinforcing previously reported data on other experimental models. Stopped-flow analysis of AE1 transport activity in red blood cell ghost preparations revealed a 50% reduction of G796R compared to WT AE1 corresponding to a loss of function of the G796R mutated protein, in accordance with the heterozygous status of the AE1 variant patients. In conclusion, stopped-flow led to measurement of rapid transport kinetics using the natural substrate for AE1, and conjugated with flow cytometry, allowed a reliable correlation of chloride/bicarbonate exchange to surface expression of AE1, both in recombinant cells and ghosts and therefore a fine comparison of function between different stomatocytosis samples. This technical approach thus provides significant improvements in anion exchange analysis in red blood cells.
- anion exchanger 1
- hereditary stomatocytosis
- stopped-flow spectrofluorometry
- red blood cells
- Copyright © 2013, American Journal of Physiology - Cell Physiology