DIFFERENTIAL OXYGEN SENSITIVITY OF THE K-CL- COTRANSPORTER IN NORMAL AND SICKLE HUMAN RED-BLOOD-CELLS()

1. K+ influx and efflux were measured in normal (HbA) and sickle (HbS) red blood cells to investigate the interaction of swelling, H+ ions a nd urea with O-2 (0 to 150 mmHg O-2) in the presence of ouabain and bu metanide (both 100 mu M). 2. In HbA cells, K+-Cl- cotransport was 0, d ependent. At low oxygen tensions (P(O2)s) the transporter was inactive and refractory to low pH, swelling or urea. 3. Cl--independent K+ inf luxes in sickle cells were elevated at low P(O2)s, as previously repor ted. Cl--dependent K+ influxes were large at both high and low P(O2)s, whether stimulated by swelling, H+ ions or urea. In the absence of O- 2, Cl--dependent K+ influxes were similar in magnitude to those measur ed at high P(O2)s. The minimum for Cl--dependent K+ influx was observe d at P(O2)s of about 40-70 mmHg. 4. K+ efflux from HbS cells was stimu lated by the addition of urea (500 mM). The rate constants were of sim ilar magnitude whether measured at high P-O2 or in the absence of O-2, and were predominantly Cl- dependent under both conditions. 5. In HbS red blood cells, reduction of extracellular Ca2+, addition of 1 mM Mg 2+ or nitrendipine (10 mu M) to the saline had no effect. Inhibitors o f K+-C-l- cotransport, [(dihydroindenyl)oxy] alkanoic acid (DIOA; 100 mu M) or calyculin A (0.1 mu M), inhibited influxes by a similar magni tude to Cl- substitution. 6. Results are significant for the pathophys iology of sickle cell disease. Low pH and urea are able to stimulate K Cl loss from sickle cells, leading to cellular dehydration, even in re gions of low P-O2.