Regulation of K-Cl cotransport during reticulocyte maturation and erythrocyte aging in normal and sickle erythrocytes.
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 approximately 33.4 g/dl) has only about approximately 5% of the KCC and 4% of the membrane (mb)-PP1 activities of the least-dense fraction (d approximately 24.7 g/dl). In sickle and normal erythrocytes, density-dependent decreases for mb-PP1 activity were similar (d50% 28.1 +/- 0.4 vs. 27.2 +/- 0.2 g/dl, respectively), whereas those for KCC activity were not (d50% 31.4 +/- 0.9 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 is higher in sickle erythrocytes, suggesting a defective, mb-PP1-independent KCC regulation. In normal, least-dense but not in densest cells, urea stimulates KCC (two- to fourfold) and moderately increases mb-PP1 (20-40%). Thus mb-PP1 appears to mediate part of urea-stimulated KCC activity.
Bize
Isabel
I
Department of Cell Biology, Harvard Medical School, 240 Longwood Ave, Boston, MA 02115, USA. isabel_bize@hms.harvard.edu
Taher
Samara
S
Brugnara
Carlo
C
D000328:Adult; D000755:Anemia, Sickle Cell / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002452:Cell Count; D016922:Cellular Senescence / Q000502:physiology; D004912:Erythrocytes / Q000166:cytology / Q000201:enzymology*; D004913:Erythrocytes, Abnormal / Q000166:cytology / Q000201:enzymology; D006801:Humans; D006982:Hypertonic Solutions / Q000494:pharmacology; D007552:Isotonic Solutions / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D011189:Potassium Chloride / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000166:cytology / Q000201:enzymology*; D027981:Symporters / Q000378:metabolism*; D014508:Urea / Q000494:pharmacology; D000096922:K Cl- Cotransporters
D006982:Hypertonic Solutions; D007552:Isotonic Solutions; D010749:Phosphoprotein Phosphatases; D011189:Potassium Chloride; D027981:Symporters; D014508:Urea; D000096922:K Cl- Cotransporters