Regulation of k-cl cotransport during reticulocyte maturation and erythrocyte aging
in normal and sickle erythrocytes.
Bize, Isabel, Samara Taher, and Carlo Brugnara.
Departments of Cell Biology, Harvard Medical School, and Department of
Laboratory Medicine, Children's Hospital Boston, Boston, Massachusetts 02115
APStracts 10:0081C, 2003.
The age/density-dependent decrease in K-Cl cotransport (KCC), PP1 and PP2A activities
in normal and sickle human erythrocytes and the effect of urea, a known KCC activator,
were studied using discontinuous, isotonic gradients. In normal erythrocytes, the densest
fraction (d ~33.4 g/dl) has only about ~5% of the KCC and 4% of the membrane (mb)-
PP1 activities of the least-dense fraction (d ~24.7 g/dl). In sickle and normal erythrocytes,
density-dependent decreases for mb-PP1 activity were similar (d50% 28.1 ± 0.4 g/dl vs.
27.2 ± 0.2 g/dl, respectively) while those KCC activity were not (d50% 31.4 ± 0.9 g/dl
vs. 26.8 ± 0.3 g/dl, respectively, P = 0.004,). Excluding the 10% least-dense cells, a very
tight correlation exists between KCC and mb-PP1 activities in normal (r2 = 0.995), and
sickle erythrocytes (r2=0.93), but at comparable mb-PP1 activities, KCC activity in
higher in sickle erythrocytes, suggesting a defective, mb-PP1 independent, KCC
regulation. In normal, least-dense but not in densest cells, urea stimulates KCC (2-4 fold)
and moderately increases mb-PP1 (20-40%). Thus mb-PP1 appears to mediate part of
urea-stimulated KCC activity.
Received 27 September 2002; accepted in final form 22 February 2003
APS Manuscript Number C447-2.
Article publication pending Am J Physiol Cell Physiol
ISSN 1080-4757 Copyright 2003 The American Physiological Society.
Published in APStracts on 25 March 2003