title: Effect of complete protein 4.1R deficiency on ion transport properties of murine erythrocytes.
abstract: Moderate hemolytic anemia, abnormal erythrocyte morphology (spherocytosis), and decreased membrane stability are observed in mice with complete deficiency of all erythroid protein 4.1 protein isoforms (4.1(-/-); Shi TS et al. J Clin Invest 103: 331, 1999). We have examined the effects of erythroid protein 4.1 (4.1R) deficiency on erythrocyte cation transport and volume regulation. 4.1(-/-) mice exhibited erythrocyte dehydration that was associated with reduced cellular K and increased Na content. Increased Na permeability was observed in these mice, mostly mediated by Na/H exchange with normal Na-K pump and Na-K-2Cl cotransport activities. The Na/H exchange of 4.1(-/-) erythrocytes was markedly activated by exposure to hypertonic conditions (18.2 +/- 3.2 in 4.1(-/-) vs. 9.8 +/- 1.3 mmol/10(13) cell x h in control mice), with an abnormal dependence on osmolality (EC(50) = 417 +/- 42 in 4.1(-/-) vs. 460 +/- 35 mosmol/kgH(2)O in control mice), suggestive of an upregulated functional state. While the affinity for internal protons was not altered (K(0.5) = 489.7 +/- 0.7 vs. 537.0 +/- 0.56 nM in control mice), the V(max) of the H-induced Na/H exchange activity was markedly elevated in 4.1(-/-) erythrocytes (V(max) 91.47 +/- 7.2 compared with 46.52 +/- 5.4 mmol/10(13) cell x h in control mice). Na/H exchange activation by okadaic acid was absent in 4.1(-/-) erythrocytes. Altogether, these results suggest that erythroid protein 4.1 plays a major role in volume regulation and physiologically downregulates Na/H exchange in mouse erythrocytes. Upregulation of the Na/H exchange is an important contributor to the elevated cell Na content of 4.1(-/-) erythrocytes.
authors.affiliation: Children's Hospital Boston, Dept. of Laboratory Medicine, Harvard Medical School, Boston, MA 02115, USA. alicia.rivera@childrens.harvard.edu
authors.forename: Alicia
authors.initials: A
authors.lastname: Rivera
authors.forename: Lucia
authors.initials: L
authors.lastname: De Franceschi
authors.forename: Luanne L
authors.initials: LL
authors.lastname: Peters
authors.forename: Philippe
authors.initials: P
authors.lastname: Gascard
authors.forename: Narla
authors.initials: N
authors.lastname: Mohandas
authors.forename: Carlo
authors.initials: C
authors.lastname: Brugnara
mesh_terms: D000818:Animals; D001798:Blood Proteins / Q000172:deficiency* / Q000378:metabolism; D002034:Bumetanide / Q000494:pharmacology; D004911:Erythrocyte Volume / Q000187:drug effects; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006982:Hypertonic Solutions / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology*; D007552:Isotonic Solutions / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008840:Microfilament Proteins; D019319:Okadaic Acid / Q000494:pharmacology; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology; D010795:Phthalic Acids / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012964:Sodium / Q000097:blood; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D027981:Symporters / Q000378:metabolism; D000096922:K Cl- Cotransporters
chemical_list: D001798:Blood Proteins; D002034:Bumetanide; D006859:Hydrogen; D006982:Hypertonic Solutions; D007552:Isotonic Solutions; D008840:Microfilament Proteins; D019319:Okadaic Acid; D010042:Ouabain; D010795:Phthalic Acids; D047428:Protein Kinase Inhibitors; D012964:Sodium; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D000254:Sodium-Potassium-Exchanging ATPase; D027981:Symporters; D000096922:K Cl- Cotransporters; C514956:Epb41 protein, mouse; C032279:phthalic acid