Effect of streptozotocin-induced diabetes on kidney Na+/K(+)-ATPase

The maximal capacity of low affinity ouabain binding sites in kidney medulla was found to be increased by 20 +/- 3.8% after 2 weeks, and by 35 +/- 4.5% in 4 weeks diabetes. However, in kidney cortex no similar changes could be detected. Western blot analysis of Na+/K(+)-ATPase subunits in kidney medulla indicated a significant enhancement of both the alpha 1 and beta 1 subunit in two and four weeks diabetic rats (alpha 1: 35 +/- 3.1, 51 +/- 5.8% and beta 1: 31.3 +/- 5.2 and 43.2 +/- 6.8%, respectively). However, kidney cortex showed no significant change in any condition tested. In diabetes we could detect a significant change only in the medulla in case of the b subunit mRNA transcript, which showed 1.69 +/- 0.59 and 2.89 +/- 0.81 times increased in two and four weeks diabetic state, respectively. There was no change in the alpha 1 subunit mRNA abundance. Insulin treatment of diabetic animals did not result in a complete reversal of diabetes-induced changes in ouabain binding capacity or in the amount of Na+/K(+)-ATPase alpha 1 and beta 1 subunit protein and mRNA levels. Our data indicate a good correlation between changes in low affinity ouabain binding capacity and the level of alpha 1 isoform in diabetic rats, and suggest an important role of the b subunit in the regulation of enzyme quantity.