title: Deoxygenation inhibits the volume-stimulated, Cl(-)-dependent K+ efflux in SS and young AA cells: a cytosolic Mg2+ modulation.
abstract: We recently reported that the Cl(-)-dependent K+ (K:Cl) efflux, which can be stimulated by cell swelling in the presence of inhibitors of the Na+ pump (ouabain) and of the Na-K-Cl cotransport (bumetanide), is highly active in young AA and SS RBCs. We report here that deoxygenation inhibits volume-stimulated K:Cl efflux in SS and reticulocyte-enriched density-separated SS and AA RBCs. In SS whole blood, the K:Cl efflux stimulated by hypotonic (220 mOsm) swelling was reduced from 9.2 +/- 2 (mean +/- SE) in oxygen to 2.7 +/- 1.9 (mmol/L cell/h = flux units = FU) (n = 4) under deoxygenated conditions (P less than .005). Deoxygenation also decreased the acid pH-stimulated K:Cl efflux from 5.9 +/- 1.5 to 3.7 +/- 1.1 FU (n = 3) (P less than .025) but did not inhibit NEM-stimulated K:Cl transport. The effect of deoxygenation on density-separated SS cells is similar: When fraction SS2 (reversible discocytes) is deoxygenated under hypotonic conditions, the K:Cl efflux is reduced by 50%. In reticulocyte-enriched AA cells obtained from anemic patients, deoxygenation under hypotonic conditions also reduces K+ efflux by 50%. In SS cells only, deoxygenation under isotonic conditions results in an increased Cl(-)-independent K+ efflux. Because ionized Mg2+ in the cytosol increases during deoxygenation, we investigated the effect of external and internal Mg2+ on the volume-stimulated K:Cl efflux. Removal of external Mg2+ did not influence the rate of transport in oxygenated cells. When internal Mg2+ was clamped at 0.15 mmol/L with A23187 and EDTA at ionized cytosolic Ca2+ = O, however, the inhibitory effect of deoxygenation on the K:Cl efflux was eliminated. We conclude that deoxygenation inhibits the volume-stimulated, Cl(-)-dependent K+ efflux in AA and SS young red cells by concomitantly increasing ionized cytosolic Mg2+.
authors: Brigham and Women's Hospital, Department of Medicine, Harvard University, Boston.
authors: M
authors: M
authors: Canessa
authors: M E
authors: ME
authors: Fabry
authors: R L
authors: RL
authors: Nagel
mesh_terms: D000755:Anemia, Sickle Cell / Q000097:blood*; D002712:Chlorides / Q000097:blood*; D003593:Cytoplasm / Q000502:physiology; D004905:Erythrocyte Aging; D004913:Erythrocytes, Abnormal / Q000502:physiology*; D006441:Hemoglobin A; D006451:Hemoglobin, Sickle; D006801:Humans; D008274:Magnesium / Q000097:blood*; D010100:Oxygen / Q000097:blood*; D011188:Potassium / Q000097:blood*; D012156:Reticulocytes / Q000502:physiology; D014882:Water-Electrolyte Balance
chemical_list: D002712:Chlorides; D006451:Hemoglobin, Sickle; D006441:Hemoglobin A; D008274:Magnesium; D011188:Potassium; D010100:Oxygen