Effects of vanadate and low potassium diet on renal H,K-ATPase and Na,K-ATPase protein expression in rat

Abstract

This study was conducted to investigate the effect of vanadate and low potassium diet on renal Na,K-ATPase and H,K-ATPase protein expression. Male Wistar rats were divided into two main groups: normal saline solution (NSS) or vanadate (V; 5 mg/kg. BW) injection. In each group, the animals were received either normal-potassium (NK) or low-potassium (LK) diet. The treatments were performed for 10 days. On each experimental due date, 24-hr urine and blood samples were collected. The serum was stored at -80 degree celsius until use for measurement of vanadium, electrolytes, blood urea nitrogen (BUN), creatinine (Cr), and Cr clearance (C[subscript cr]). The kidneys were removed and fixed for measurement of Na,K-ATPase as well as H,K-ATPase ([alpha]1 and [alpha]2 isoforms) protein expression. Some renal tissue samples also were determined for vanadium concentration. Ten days of vanadate administration significantly increased vanadium levels in serum, urine,and renal tissues in both NK and LK groups. By immunohistochemistry, the expression of renal Na,K-ATPase protein showed the main staining in distal tubule and collecting duct both in cortex and medulla. The expression was increased by LK but was reduced by V. LK in V treated rats could not restore the expression. For H,K-ATPase, in cortex, LK could enhance the protein expression of both [alpha]1- and [alpha]2-subunit at luminal membrane of collecting duct. In medulla, LK slightly increased [alpha]1-isofrom protein expression, whereas no expression of [alpha]2 was noted. Vanadate did not affect on H,K-ATPase protein expression both [alpha]1 and [alpha]2. Administration of both V and LK caused a progressive hypokalemia as well as induced azotemia and natriuresis. LK in either NSS or V treated rats significantly reduced blood pCO[subscript 2] while blood pH was remained normal. Treatment of V in LK animals increased fractional excretion of potassium, chloride, and bicarbonate. All experimental rats showed no significant changes in urine flow rate. The present data are the first evidence showing that LK could not restore the suppressive effect of V on renal Na,K-ATPase protein expression. Vanadate has no influence on renal H,K-ATPase protein expression. However, LK still plays an important stimulus to increase H,K-ATPase protein expression both [alpha]1 and [alpha]2 isoforms. Combination treatment of V and LK caused more profound alterations in metabolic parameter as well as renal function than those subjected to either V or LK alone.