Effects of Chronic Hypokalemia on Renal Expression of Na/K-APTase alpha1 and beta1 Subunit

Ahn, Kyu Youn; Moon, Boung Cheon; Heo, Tag; Min, Yong Il

Abstract

To depend body potassium balance during chronic hypokalemia, the kidney actively reabsorbs potassium. Previous work suggested that potassium reclamation occurred at the distal tubule and collecting duct. We used immunohistochemistry of normal and potassium-deprived(two weeks) rats to determine the intrarenal distribution and alteration of expression of Na/K-ATPase alpha1 and beta1 subunit protein and also whether the increased numbers of both subunits reside in the apical or basolateral membranes. In the normal rats, alpha1 and beta1 immunoreactivity was prominent in the medullary and cortical thick ascending limb, distal convoluted tubule, and connecting segment. Cortical collecting duct, glomerular epithelial cell, and intraglomerular mesangial cell exhibited moderate immunoreactivity, whereas proximal tubule and medullary collecting duct were weakly labeled in alpha1 subunit. In beta1 subunit, cortical collecting duct and proximal tubule exhibited moderate immunoreactivity, and medullary collecting duct was very weakly labeled. In the K-deprived rats, a pattern of cellular labeling of both subunits was identical to that of normal rats. Marked increases of immunoreactivity were evident in the inner stripe of the outer medullary collecting duct and proximal portion of the inner medullary collecting duct. In these segment, alpha1 and beta1 immunoreactivity was expressed at the basolateral pole, and no apical expression was detected. In contrast, immunoreactivity of the medullary and cortical thick ascending limb, distal convoluted tubule, connecting segment, and cortical collecting duct was decreased. These results suggest that Na/K-ATPase alpha1 and beta1 subunit are differentially expressed in different nephron segments and chronic hypokalemia must also upregulate K exit pathways in the basolateral membrane of inner stripe of the outer medullary collecting duct and proximal portion of the inner medullary collecting duct to promote recycling and limit secretion of K.