Normal Ca2+ extrusion by the Ca2+ pump of intact red blood cells exposed to high glucose concentrations

The ATPase activity of the plasma membrane Ca2+ pump (PMCA) has been report ed to be inhibited by exposure of red blood cell (RBC) PMCA preparations to high glucose concentrations. It has been claimed that this effect could ha ve potential pathophysiological relevance in diabetes. To ascertain whether high glucose levels also affect PMCA transport function in intact RBCs, Ca 2+ extrusion by the Ca2+-saturated pump [PMCA maximal velocity (V-max)] was measured in human and rat RBCs exposed to high glucose in vivo or in vitro . Preincubation of normal human RBCs in 30-100 mM glucose for up to 6 h had no effect on PMCA V-max. The mean V-max of RBCs from 15 diabetic subjects of 12.9 +/- 0.7 mmol.340 g Hb(-1) . h(-1) was not significantly different f rom that of controls (14.3 +/- 0.5 mmol.340 g Hb(-1).h(-1)). Similarly, the PMCA Vmax of RBCs from 11 streptozotocin-diabetic rats was not affected by plasma glucose levels more than three times normal for 6-8 wk. Thus exposu re to high glucose concentrations does not affect the ability of intact RBC s to extrude Ca2+.