ENaC And NKCC2 Expression In Kidney Of Rat With Adenine Induced Chronic Renal Failure

Kidneys are the ones of the most important organs in body. The main renal physiological function includes excreting metabolites and regulation of water, electrolyte and acid-base balance, as well as maintaining the homeostasis. The different sodium transporters and water channels which distribute in epithelial cells of renal tubular and collecting duct play roles in the body fluid balance and maintenance of the homeostasis. These proteins expression level and functional status play an important role in water reabsorption and sodium reabsorption. The NKCC2 is mainly expressed in renal medullary thick ascending limb as well as the macula densa. The NKCC2 is responsible for the reabsorption of NaCl in medullary thick ascending loop segment and the urinary concentration. ENaC located in connecting tubule principal cells and collecting duct epithelial cells is responsible for a small amount of sodium reabsorption, but ENaC is the critical rate-limiting step in renal reabsorption of sodium. AQP2, the important renal water channel protein, is mainly expressed in the epithelial cell of collecting duct near inner renal medulla. The water reabsorption of AQP2 was regulated by Antidiuretic hormone(ADH). These channel proteins have to expresse at the apical membrane for reabsortption through special trafficking mechanism. The function and activity of these channels is determined by theirs amount, but also the relevant location in renal tubular cells.Chronic Renal Failure Progressive Reduction in Renal Function Resulting in the Retention of Nitrogenous SubstancesChronic renal failure is characterized by a variety of abnormalities following of the progressive course of different primary and secondary renal disease. Chronic renal failure can present a persistent decrease in total number of nephrons or renal function, until resulting in renal insufficiency and finally terminal stage renal failure syndrome. Based on the degree of renal damage, chronic renal failure can be divided into different periods, compensated renal insufficiency, decompensated azotemia period and the advanced renal failure stage as well as uremia. There is no doubt that chronic renal failure is resulted from various renal disease, but progressive deterioration mechanism of chronic renal failure is not completely clear yet. Some chronic renal failure symptoms, such as polyuria and water and electrolyte imbalance, are absolutely concerned with the abnormal renal reabsorption of salt and water. Perhaps its mechanism is related to the abnormal distribution of channel protein in different segments. The major renal sodium channel proteins, NKCC2 and ENaC, are distributed in the ascending Henle's loop and distal convoluted connecting tubule respectively. Their altered expression may play a major role in the pathogenesis of chronic renal failure. At the same time, polyuria may probably be induced by the deacrease of AQP2's water reabsorption.Objective:In this study, we establish chronic renal failure rat model induced with adenine. We determine the NKCC2 andγ-ENaC expression in the renal epithelial cell of rat with chronic renal failure, and explain the mechanism of disorder of water and sodium metabolism.Methods:In this study, the serum and urine biochemical factors were analyzed, the urine volume and bodyweight of rats were measured and renal morphological change was observed with hematoxylin and eosin and Masson staining methods. The mRNA and protein of NKCC2 andγ-ENaC expression was detected with RT-PCR, Western blotting and immunohistochemical staining methods. We also detected the level of mRNA AQP2 by RT-PCR.Results:It was found that the urine volume increases and the bodyweight decreases in rats with chronic renal failure. Serum sodium and chloride concentration decreases, but serum potassium concentration increases, serum urea nitrogen also increases, but serum creatinine decreases when compared with control rats. The ions concentration in urine are parallel with that in serum. The severe damage in renal tubular and renal interstitial fibrosis can be found in the kidney tissues by morphological observation. The mRNA level of NKCC2and AQP2 decreases in chronic renal failure rats when compared with controls, but the mRNA level ofγ-ENaC is higher than that in control group. NKCC2 andγ-ENaC protein expression also decreases. The results of immunohistochemical staining have confirmed the Western Blotting results further, and it also shows the location of NKCC2 andγ-ENaC primarily in the cytoplasm.Conclusion:We have successfully established the chronic renal failure rat model induced with adenine, and this can be confirmed with the results of body weight, urine volume, the morphological changes and urine and serum biochemical factors. The chronic renal failure is a progressive process from compensation to decompensation. The disorder of renal tubular reabsorption precedes that of glomerular filtration in chronic renal failure rats. The expression of NKCC2,γ-ENaC and AQP2 decreases in chronic renal failure rats. The diminished amount of these channels is one of the reasons which results in polyuria and hyponatremia.