Abnormal permeability pathways in human red blood cells

A number of situations that result in abnormal permeability pathways in human red blood cells (RBCs) have been investigated. In sickle cell disease (SCD), RBCs contain HbS, rather than the normal HbA. When deoxygenated, an abnormal conductance pathway, termed P(sickle), is activated, which contributes to cell dehydration, largely through allowing Ca(2+) entry and subsequent activation of the Gardos channel. Whole-cell patch-clamp recordings from sickle RBCs show a deoxygenated-induced conductance, absent from normal RBCs, which shares some of the properties of P(sickle): equivalent Na(+) and K(+) permeability, significant Ca(2+) conductance, partial inhibition by DIDS and also Zn(2+). Gd(3+) markedly attenuates conductance in both normal and sickle RBCs. In addition, deoxygenated sickle cells, but not oxygenated ones or normal RBCs regardless of the oxygen tension, undergo haemolysis in isosmotic non-electrolyte solutions. Non-electrolyte entry was confirmed radioisotopically whilst haemolysis was inhibited by DIDS. These findings suggest that under certain circumstances P(sickle) may also be permeable to non-electrolytes. Finally, RBCs from certain patients with hereditary stomatocytosis have a mutated band 3, which appears able to act as a conductance pathway for univalent cations. These results extend our understanding of the abnormal permeability pathways of RBCs.