Inhibition of erythrocyte cation channels by erythropoietin.
Recombinant human erythropoietin therapy is used to counteract anemia that is the result of renal insufficiency. It stimulates the formation of peripheral blood erythrocytes by inhibiting apoptosis of erythrocyte precursor cells. Mature erythrocytes have similarly been shown to undergo apoptosis. Hyperosmotic shock and Cl(-) removal activate a Ca(2+)-permeable, ethylisopropylamiloride-inhibitable cation channel. The subsequent increase of cytosolic Ca(2+) activates a scramblase that breaks down cell membrane phosphatidylserine asymmetry, leading to annexin binding. Studied was whether channel activity and erythrocyte cell death are regulated by erythropoietin. Scatchard plot analysis disclosed low-abundance, high-affinity binding of (125)I-erythropoietin to erythrocytes. Whole cell patch clamp experiments revealed significant inhibition of the ethylisopropylamiloride-sensitive current by 1 U/ml erythropoietin. Cl(-) removal triggered annexin binding, an effect abrogated by erythropoietin (1 U/ml) but not by GM-CSF (10 ng/ml). Osmotic shock (700 mOsm) stimulated annexin binding within 24 h in the majority of the erythrocytes, an effect blunted by erythropoietin (1 U/ml) but not by GM-CSF (10 ng/ml). In the nominal absence of Ca(2+), the effect of osmotic shock was blunted and the effect of erythropoietin abolished. In hemodialysis patients, intravenous administration of erythropoietin (50 IU/kg) within 4 h decreased the number of annexin binding circulating erythrocytes. Erythropoietin binds to erythrocytes and inhibits volume-sensitive erythrocyte cation channels and thus the breakdown of phosphatidylserine asymmetry after activation of this channel. The effect could prolong the erythrocyte lifespan and may contribute to the enhancement of the erythrocyte number during erythropoietin therapy in dialysis patients.
Myssina
Svetlana
S
Department of Physiology, University of Tübingen, Germany.
Huber
Stephan M
SM
Birka
Christina
C
Lang
Philipp A
PA
Lang
Karl S
KS
Friedrich
Björn
B
Risler
Teut
T
Wieder
Thomas
T
Lang
Florian
F
D017304:Annexin A5 / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D018929:Cell Culture Techniques; D004789:Enzyme Activation; D004912:Erythrocytes / Q000378:metabolism*; D004921:Erythropoietin / Q000502:physiology*; D045604:Extracellular Fluid / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D009997:Osmotic Pressure; D018408:Patch-Clamp Techniques; D049294:Phospholipid Transfer Proteins; D011485:Protein Binding / Q000502:physiology*
D017304:Annexin A5; D015220:Calcium Channels; D002352:Carrier Proteins; D008565:Membrane Proteins; D049294:Phospholipid Transfer Proteins; D004921:Erythropoietin