Altered expression of renal NHE3, TSC, BSC-1, and ENaC subunits in potassium-depleted rats

Abstract

The purpose of this study was to examine whether hypokalemia is associated with altered abundance of major renal Na+ transporters that may contribute to the development of urinary concentrating defects. We examined the changes in the abundance of the type 3 Na+/H+ exchanger (NHE3), Na+-K+-ATPase, the bumetanide-sensitive Na+-K+-2Cl− cotransporter (BSC-1), the thiazide-sensitive Na+-Cl− cotransporter (TSC), and epithelial sodium channel (ENaC) subunits in kidneys of hypokalemic rats. Semiquantitative immunoblotting revealed that the abundance of BSC-1 (57%) and TSC (46%) were profoundly decreased in the inner stripe of the outer medulla (ISOM) and cortex/outer stripe of the outer medulla (OSOM), respectively. These findings were confirmed by immunohistochemistry. Moreover, total kidney abundance of all ENaC subunits was significantly reduced in response to the hypokalemia: α-subunit (61%), β-subunit (41%), and γ-subunit (60%), and this was confirmed by immunohistochemistry. In contrast, the renal abundance of NHE3 in hypokalemic rats was dramatically increased in cortex/OSOM (736%) and ISOM (210%). Downregulation of BSC-1, TSC, and ENaC may contribute to the urinary concentrating defect, whereas upregulation of NHE3 may be compensatory to prevent urinary Na+ loss and/or to maintain intracellular pH levels.

Long-term aldosterone treatment induces decreased apical but increased basolateral expression of AQP2 in CCD of rat kidney

“…Ten-day exposure to low potassium diet-induced hypokalemia has been demonstrated to decrease renal AQP2 expression and decreased urinary concentration (20). As aldosterone-treated rats might have suffered hypokalemia for a shorter period, the immunohistochemistry of rats exposed to 4 days of a low-potassium diet was studied (8). Rats treated with a potassium-deficient diet for 4 days had weaker apical AQP2 labeling compared with control rats in CCDs (Fig.…”

“…Protocol 4: low-potassium diet-induced hypokalemia in rats with low levels of plasma aldosterone. Given the presence of hypokalemia in the aldosterone-treated rats and the potential effect of this factor on AQP2 regulation, we investigated the distribution of AQP2 in the CCD of hypokalemic rats induced by potassium restriction, who have a low plasma aldosterone level (8). Kidney sections from 4-day hypokalemic rats were used.…”

“…Kidney sections from 4-day hypokalemic rats were used. Regulation of other transporters was previously described in these rats (8). Rats were randomized into two groups matched for body weight: a hypokalemic group (n ϭ 12) and a control group (n ϭ 12).…”

“…Thus the food intake was matched between the two groups. Rats in both groups had free access to water throughout the experiment (8).…”

Angiotensin II AT1receptor blockade decreases vasopressin-induced water reabsorption and AQP2 levels in NaCl-restricted rats

“…An increase in the delivery of NaCl to the loop of Henle by chronic oral saline loading (12) or DDAVP treatment in Brattleboro rats (28) has been demonstrated to upregulate NKCC2 levels, whereas hypokalemia-induced nephrogenic diabetes insipidus (13) or parathyroid hormone-induced hypercalcemia (58) was associated with reduced NKCC2 expression along with decreased urine concentration. Vasopressin is generally believed to play an important role in NaCl reabsorption in the TAL, which could be mediated by V 2 receptors, adenylyl cylase, and cAMP (5,16,31).…”