The
resting membrane potential of the human erythrocyte is largely determined by a constitutive Cl
− conductance 100-fold greater than the
resting cat
ion conductance. The 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS)-sensitive electroneutral Cl
− transport mediated by the human erythroid Cl
−/HCO
3− exchanger, AE1 (SLC4A1, band 3) is > 10,000-fold greater than can be accounted for by the Cl
− conductance of the red cell. The molecular identities of conductive an
ion pathways across the red cell membrane remain poorly defined. We have examined red cell Cl
− conductance in the
Ae1−/− mouse as a genetic test of the hypothesis that Ae1 mediates DIDS-sensitive Cl
− conductance in mouse red cells. We report here that wildtype mouse red cell membrane potential resembles that of human red cells in the predominance of its Cl
− conductance. We show with four technical approaches that the DIDS-sensitive component of erythroid Cl
− conductance is reduced or absent from
Ae1−/− red cells. These results are consistent with the hypothesis that the Ae1 an
ion exchanger polypeptide can operate infrequently in a conductive mode. However, the fragile red cell membrane of the
Ae1−/− mouse red cell exhibits reduced abundance or loss of multiple polypeptides. Thus, loss of one or more distinct, DIDS-sensitive an
ion channel polypeptide(s) from the
Ae1−/− red cell membrane cannot be ruled out as an explanat
ion for the reduced DIDS-sensitive an
ion conductance.