Sodium transport across erythrocyte membranes in diabetes mellitus

The activity of the erythrocyte ouabain sensitive Na/K ATPase pump was studied in 20 Type 1 diabetics, 15 Type 2 diabetics and 20 healthy controls. All diabetics were normotensive, caucasian and non-obese diabetics. The diabetics were assessed for retinopathy and had HbA1 estimated. The erythrocyte sodium concentration, membrane permeability to sodium and ouabain-sensitive sodium efflux rate constant (ERCos) were determined. The Type 1 diabetics had a significantly reduced ERC, mean +/- SD 0.198 +/- 0.028 hr-1 vs control 0.264 +/- 0.054 hr-1 (p less than 0.001). A similar reduction in ERCos was seen in the Type 2 diabetics when compared to controls (0.229 +/- 0.059 hr-1 p less than 0.005). There was also a significant difference between the 2 groups of diabetics (p less than 0.05). There was no significant difference in intracellular sodium concentrations. Membrane permeability was reduced in the Type 1 diabetics (3.69 +/- 0.79 mmol/kg dry wt/hr) compared to the control group (4.56 +/- 0.79 mmol/kg dry wt/hr, p less than 0.01). Diabetic control (HbA1) was positively correlated with ERCos, but no significant differences were seen in the ERCos between complicated and uncomplicated Type 1 diabetics. In vitro studies of normal erythrocytes did not show an effect on pump activity of increasing glucose or insulin concentration during a preincubation study. These results demonstrate that there is a reduction in activity of the ouabain-sensitive Na/K ATPase pump and a reduction in membrane permeability on the diabetic erythrocyte which is most marked in Type 1 diabetics.