title: Increased cation permeability in mutant mouse red blood cells with defective membrane skeletons.
abstract: Cellular cation homeostasis in mouse erythrocytes with defective membrane skeletons was examined in three mouse mutants, hemolytic anemia (sphha/sphha), spherocytosis (sph/sph), and normoblastosis (nb/nb), and compared with reticulocytes produced by repetitive bleeding of congenic normal mice. To assess reticulocyte maturity, nucleic acid and transferrin receptor contents were measured by fluorescence flow cytometry; mutant cells were somewhat more mature than normal reticulocytes by these criteria. Red blood cell (RBC) sodium contents (Nac+) in homozygous sphha/sphha, sph/sph, and nb/nb animals were 30.1 +/- 0.9, 28.9 +/- 0.3, and 26.9 +/- 1.5 mmol/L cell, respectively, whereas cellular potassium (Kc+) was 102 +/- 2.6, 101 +/- 7.8, and 97.4 +/- 3.0. Nac+ and Kc+ in normal reticulocyte preparations were 11.3 +/- 0.7 and 123 +/- 10, respectively. Net Na+ and K+ fluxes in the presence of ouabain were markedly increased in mutant RBCs. Sodium uptake was 14.8 +/- 1.6, 15.4 +/- 3.3, and 14.7 +/- 3.1 mmol/L cell/h in sphha/sphha, sph/sph, and nb/nb mutants, respectively, whereas K+ loss was 17.0 +/- 4.0, 15.0 +/- 3.8, and 14.1 +/- 2.6. Normal mouse reticulocytes gained Na+ at a rate of 3.9 +/- 1.0 mmol/L cell/h and lost K+ at 6.0 +/- 2.1, rates indistinguishable from those in mature mouse RBCs. Potassium loss from sphha/sphha and nb/nb cells was not dependent on the presence of a Na+ gradient, and net cation movements were insensitive to bumetanide (sphha/sphha and nb/nb RBCs) and to chloride replacement with sulfamate (nb/nb cells). We conclude that mutant mouse RBCs with dysfunctional membrane skeletons have increased passive permeability to monovalent cations. These findings support a role of the membrane skeleton in the maintenance of the membrane permeability barrier and suggest that the abnormal permeability associated with human hereditary spherocytosis and elliptocytosis may be a consequence of the membrane skeleton defects reported in these disorders.
mesh_terms: D000743:Anemia, Hemolytic / Q000097:blood / Q000235:genetics; D000818:Animals; D001693:Biological Transport, Active; D003599:Cytoskeleton / Q000187:drug effects; D004899:Erythroblastosis, Fetal / Q000097:blood / Q000235:genetics; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006706:Homeostasis; D006801:Humans; D007231:Infant, Newborn; D051379:Mice; D008817:Mice, Mutant Strains; D010539:Permeability; D011188:Potassium / Q000097:blood*; D012156:Reticulocytes / Q000378:metabolism; D012964:Sodium / Q000097:blood*; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood / Q000235:genetics; D013103:Spherocytosis, Hereditary / Q000097:blood / Q000235:genetics
chemical_list: D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium