Effect of complete protein 4.1R deficiency on ion transport properties of murine erythrocytes.
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.
Rivera
Alicia
A
Children's Hospital Boston, Dept. of Laboratory Medicine, Harvard Medical School, Boston, MA 02115, USA. alicia.rivera@childrens.harvard.edu
De Franceschi
Lucia
L
Peters
Luanne L
LL
Gascard
Philippe
P
Mohandas
Narla
N
Brugnara
Carlo
C
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
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