Evaluation of sodium and potassium pump activity and number in diabetic erythrocytes

The Na+,K+-ATPase (= Na pump), which produces the concentration gradient of Na+ and K+ across the cell membrane, was studied in diabetic erythrocytes. The activity and number of Na pumps, which are functional and quantitative expression of the Na+,K+-ATPase in erythrocytes, were measured by ouabain-sensitive 42K or 43K influx and by [3H]ouabain binding, respectively. The turnover rate of the pumps was calculated from the two measurements to evaluate in situ activity of the pump. The Na pump activity was found to be higher in the diabetic (193 +/- 12 nmol K+/h . 10(9) cells) than in the normal group (164 +/- 6) (P less than 0.05), though the affinities of the pump for extracellular K+ were not different. The number of Na pumps and the Kd of the pumps for ouabain in the diabetic group were not significantly different from those in the normal group (354 +/- 12 site/cell and 4.33 +/- 0.20 nM). The turnover rate of the diabetic group tended to be higher than that of the normal group. The rate was about one third of the molecular activity reported for Na+,K+-ATPase under optimum conditions. These results indicate that the enzymatic properties as well as the number of Na pumps were not altered in diabetic erythrocytes despite the increased Na pump activity. Therefore the increased activity of the erythrocyte Na pump in diabetes mellitus suggests an increase of cation permeability associated with a possible disorder in the diabetic membrane.