Ion channels in human erythroblasts. Modulation by erythropoietin.
To investigate the mechanism of intracellular Ca2+ ([Cai]) increase in human burst-forming unit-erythroid-derived erythroblasts by erythropoietin, we measured [Cai] with digital video imaging, cellular phosphoinositides with high performance liquid chromatography, and plasma membrane potential and currents with whole cell patch clamp. Chelation of extracellular free Ca2+ abolished [Cai] increase induced by erythropoietin. In addition, the levels of inositol-1,4,5-trisphosphate did not increase in erythropoietin-treated erythroblasts. These results indicate that in erythropoietin-stimulated cells, Ca2+ influx rather than intracellular Ca2+ mobilization was responsible for [Cai] rise. Both Ni2+ and moderately high doses of nifedipine blocked [Cai] increase, suggesting involvement of ion channels. Resting membrane potential in human erythroblasts was -10.9 +/- 1.0 mV and was not affected by erythropoietin, suggesting erythropoietin modulated a voltage-independent ion channel permeable to Ca2+. No voltage-dependent ion channel but a Ca(2+)-activated K+ channel was detected in human erythroblasts. The magnitude of erythropoietin-induced [Cai] increase, however, was insufficient to open Ca(2+)-activated K+ channels. Our data suggest erythropoietin modulated a voltage-independent ion channel permeable to Ca2+, resulting in sustained increases in [Cai].
Cheung
J Y
JY
Department of Medicine, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
Elensky
M B
MB
Brauneis
U
U
Scaduto
R C
RC
Bell
L L
LL
Tillotson
D L
DL
Miller
B A
BA
D000328:Adult; D002118:Calcium / Q000378:metabolism; D004900:Erythroblasts / Q000187:drug effects* / Q000378:metabolism*; D004921:Erythropoietin / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000032:analysis; D007473:Ion Channels / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects
D007473:Ion Channels; D015221:Potassium Channels; D004921:Erythropoietin; D015544:Inositol 1,4,5-Trisphosphate; D009543:Nifedipine; D002118:Calcium