Reversible sodium pump defect and swelling in the diabetic rat erythrocyte: effects on filterability and implications for microangiopathy.

Abstract

We have found a defect in the ouabain-sensitive Na+,K+-ATPase (Na+ pump, EC 3.6.1.37) oferythrocytes from streptozotocin diabetic rats. This defect was accompanied by an increase in cell volume and osmotic fragility and a decrease in the cytosolic K+/Na+ ratio. There was also a doubling in the time needed for diabetic erythrocytes to pass through 4.7-jim channels in a polycarbonate filter. Our data are consistent with a primary defect in the erythrocyte Na+ pump and secondary changes in cell volume, osmotic fragility, K+/Na+ ratio, and cell ifiterability. All were reversed or prevented in vivo by insulin or the aldose reductase inhibitor Sorbinil. Protein kinase C agonists (phorbol ester and diacylglycerol) and agonist precursor (myoinositol) reversed the Na+ pump lesion, suggesting that protein kinase C-dependent phosphorylation of the 100-kDa subunit regulates Na+ pump activity and that insulin can influence erythrocyte protein kinase C activity. Ouabain inhibition of the erythrocyte Na+ pump also produced increases in cell size and reductions in rates of ifitration. Theoretical treatment of the volume changes also predicts reduction in ifiterability as a consequence of cell swelling. We suggest that enlarged erythrocytes could play a role in the evolution of the microvascular changes of diabetes mellitus.A decrease in ouabain-sensitive Na',K+-ATPase (Na' pump, EC 3.6.1.37) activity has been found in diabetic lens, nerve, and glomerulus (1-3). This Na' pump impairment was corrected by aldose reductase inhibitors or by normalization of blood sugar with insulin. In contrast, Na' pump activity in diabetic erythrocytes (RBCs) is a subject of controversy, with reports of increases (4, 5) and decreases (6, 7). We therefore initiated a study of the Na' pump in erythrocytes of rats rendered diabetic with streptozotocin. The streptozotocin diabetic rat provided a reliable source ofRBCs whose time-integrated exposure to hyperglycemia was determined by measurement of glycated albumin. Since nondiabetic RBCs must deform considerably to pass through small capillaries, we were especially interested in learning whether such a putative Na' pump lesion would influence the volume and hence filterability of affected RBCs. MATERIALS

In vivo phosphorylation of the Na,K-ATPase alpha subunit in sciatic nerves of control and diabetic rats: effects of protein kinase modulators.

“…Published results based on indirect approaches are, however, conflicting. On the one hand, the acute application of PKC activators specifically corrected the impaired activity of the pump in peripheral nerves (10,12,13) and in erythrocytes of diabetic animals (14). On the other hand, altered Na,K-ATPase activity in sciatic nerves of diabetic mice was apparently increased by inhibitors of PKC (15,16).…”

Age-Associated Changes in Histology and Gene-Expression Profile in the Rat Ventral Prostate

“…These include those affecting galactose metabolism, pentose phosphate oxidation, oxidative phosphorylation, Na/K-ATPase activity, and citrate/isocitrate utilization. Na/K-ATPase activity, localized on the cell membrane, regulates cell volume and consumes a significant amount of cellular energy (Kowluru et al, 1989). It has been shown to undergo age-related declines in other bodily organs (Lenaz et al, 2000).…”

Noninvasive Evaluation of Kidney Hypoxia and Fibrosis Using Magnetic Resonance Imaging

“…16 These results suggest the existence of other factors, such as impairment of oxygen diffusion in the interstitium, inability of tubule-epithelial cells to utilize oxygen, or abnormal oxy- gen affinity in diabetic red blood cells, which contribute to cellular hypoxia under conditions of hyperglycemia. 17 Moreover, amelioration of oxidative stress improved renal oxygenation in an animal model of diabetic nephropathy. 18,19 Oxidative stress can stimulate tissue hypoxia via depletion of nitric oxide without inducing any apparent histologic changes.…”