and Na+ transport in RBCs from control mice (C57Bl/6J) and a transgenic (αHβS[βMDD]) mouse line that expresses high levels of human αH and βS-chains and has a small percent dense cells but does not exhibit anemia. In transgenic mouse RBCs (n= 5) under oxygenated conditions, K+ efflux was 0.22 ± 0.01 mmol/L cell × min and Na+ influx was 0.17 ± 0.02 mmol/L cell × min. Both fluxes were stimulated by 10 min deoxygenation in transgenic but not in control mice. The deoxy-stimulated K+ efflux from transgenic mouse RBCs was about 55% inhibited by 5 nm charybdotoxin (CTX), a blocker of the calcium activated K+-channel. To compare the fluxes between human and mouse RBCs, we measured the area of mouse RBCs and normalized values to area per liter of cells. The deoxy-simulated CTX-sensitive K+ efflux was larger than the CTX-sensitive K+ efflux observed in RBCs from SS patients. These results suggest that in transgenic mice, deoxygenation increases cytosolic Ca2+ to levels which open Ca2+-activated K+ channels. The presence of these channels was confirmed in both control and transgenic mice by clamping intracellular Ca2+ at 10 μm with the ionophore A23187 and measuring Ca2+-activated K+ efflux. Both types of mouse had similar maximal rates of CTX-sensitive, Ca2+-activated K+ efflux that were similar to those in human SS cells. The capacity of the mouse red cell membrane to regulate cytosolic Ca2+ levels was examined by measurements of the maximal rate of calmodulin activated Ca2+-ATPase activity. This activity was 3-fold greater than that observed in human RBCs thus indicating that mouse RBC membranes have more capacity to regulate cytosolic Ca2+ levels.
The Journal of Membrane Biology – Springer Journals
Published: Oct 1, 1997
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