Differential effect of HOE642 on two separate monovalent cation transporters in the human red cell membrane

Residual K+ fluxes in red blood cells can be stimulated in conditions of low ionic strength. Previous studies have identified both the non- selective, voltagedependent cation ( NSVDC) channel and the K+( Na+)/ H+ exchanger as candidate pathways mediating this effect, although it is possible that these pathways represent different modes of operation of a single system. In the present study the effects of HOE642, recently characterised as an inhibitor of the K+( Na+)/ H+ exchanger, on NSVDC has been determined to clarify this question. Radioisotope flux measurements and conductance determinations showed that HOE642 exerted differential effects on the NSVDC channel and the K+( Na+)/ H+ exchanger, confirming that the salt loss observed in low ionic strength solutions represents contributions from at least two independent ion transport pathways. The findings are discussed in the context of red blood cell apoptosis ( eryptosis) and disease.