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 reported to be inhibited by exposure of red blood cell (RBC) PMCA preparations to high glucose concentrations. It has been claimed that this effect could have potential pathophysiological relevance in diabetes. To ascertain whether high glucose levels also affect PMCA transport function in intact RBCs, Ca²⁺ 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 from that of controls (14.3 ± 0.5 mmol.340 g Hb^-1·h^-1). Similarly, the PMCA V_max of RBCs from 11 streptozotocin-diabetic rats was not affected by plasma glucose levels more than three times normal for 6-8 wk. Thus exposure to high glucose concentrations does not affect the ability of intact RBCs to extrude Ca²⁺.