Modulation of calcium channels in human erythroblasts by erythropoietin
JY Cheung, XQ Zhang, K Bokvist, DL Tillotson and BA Miller
Department of Medicine, Milton S. Hershey Medical Center, Pennsylvania
State University, Hershey, USA.
Erythropoietin (Epo) induces a dose-dependent increase in intracellular
free Ca2+ ([Ca2+]i) in human erythroblasts, which is dependent on
extracellular Ca2+ and blocked by high doses of nifedipine or Ni2+. In
addition, pretreatment of human erythroblasts with mouse antihuman
erythropoietin receptor antibody but not mouse immunopure IgG blocked the
Epo-induced [Ca2+]i increase, indicating the specificity of the Ca2+
response to Epo stimulation. In this study, the erythropoietin- regulated
calcium channel was identified by single channel recordings. Use of
conventional whole cell patch-clamp failed to detect Epo-induced whole cell
Ca2+ current. To minimize washout of cytosolic constituents, we next used
nystatin perforated patch, but did not find any Epo- induced whole cell
Ca2+ current. Using Ba2+ (30 mmol/L) as charge carrier in cell-attached
patches, we detected single channels with unitary conductance of 3.2 pS,
reversal potential of +72 mV, and whose unitary current (at +10 mV)
increased monotonically with increasing Ba2+ concentrations. Channel open
probability did not appreciably change over the voltage range (-50 to +30
mV) tested. Epo (2 U/mL) increased both mean open time (from 4.27 +/- 0.75
to 11.15 +/- 1.80 ms) and open probability (from 0.26 +/- 0.06 to 2.56 +/-
0.59%) of this Ba(2+)-permeable channel. Our data strongly support the
conclusion that the Epo-induced [Ca2+]i increase in human erythroblasts is
mediated via Ca2+ entry through a voltage-independent Ca2+ channel.
Volume 89,
Issue 1,
pp. 92-9100,
01/01/1997
Copyright © 1997 by The American Society of Hematology
