Deoxygenation-induced cation fluxes in sickle cells iv. modulation
by external calcium..
Joiner, Clinton H., Maorong Jiang, and Robert S. Franco.
Departments of Pediatrics, Physiology and Biophysics, and Internal
Medicine, University of Cincinnati College of Medicine, Children's
Hospital Medical Center, Cincinnati Comprehensive Sickle Cell Center,
Cincinnati, Ohio
APStracts 2:0095C, 1995.
Net cation movements were measured in low density sickle red blood
cells (SS RBC) in the presence and absence of oxygen. External Ca++
(Cao++) partially inhibited deoxygenation-induced fluxes of both Na+
and K+. Deoxygenation-induced Na+ influx was reduced by 2 mM Cao++ to
0.71 +/- 0.04 (SEM) of its value in Ca++-free solutions, whereas this
ratio was 0.90 +/- 0.05 for K+ efflux (p<0.01 by paired t-test). Since
Cao++ inhibited Na+ influx more than K+ efflux, net cation loss in
deoxygenated SS RBC was higher in the presence of Cao++. In separate
experiments, Cao++ reduced deoxygenation-induced Na+ influx to 0.66 +/-
0.03 of its Ca++-free value compared to 0.77 +/- 0.03 for Rb+ influx
(p< 0.001), indicating relative selectivity of this effect for Na+
over Rb+. However, this effect is not specific for Ca++, as other
divalent cations also inhibited deoxygenation-induced Na+ and K+
fluxes. Under the conditions of these experiments, no evidence for K+
channel activation was found, indicating that K+ loss measured in
deoxygenated SS RBC was mediated by the deoxygenation-induced
pathway. These studies show that in the presence of Cao++,
deoxygenation-induced Na+ influx and K+ efflux are unbalanced. This
pathway can, therefore, mediate cation loss and contribute directly
to cellular dehydration in SS RBC.
Received 17 November 1994; accepted in final form 13 January
1995.
APS Manuscript Number C675-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 28 February 1995.