Animals ; Calpain ; metabolism ; Epithelial Cells ; metabolism ; Kidney ; cytology ; Kidney Tubules ; cytology ; metabolism ; Rats ; Reperfusion Injury ; metabolism

Basolateral inwardly-rectifying K channels (Kir) play an important role in the control of resting membrane potential and transepithelial voltage, thereby modulating water and electrolyte transport in the distal part of nephron. Kir4.1 and Kir4.1/Kir5.1 heterotetramer are abundantly expressed in the basolateral membrane of late thick ascending limb (TAL), distal convoluted tubule (DCT), connecting tubule (CNT) and cortical collecting duct (CCD). Loss-of-function mutations in KCNJ10 cause EAST/SeSAME syndrome in humans associated with epilepsy, ataxia, sensorineural deafness and water-electrolyte metabolism imbalance, which is characterized by salt wasting, hypomagnesaemia, hypokalaemia and metabolic alkalosis. In contrast, mice lacking Kir5.1 have severe renal phenotype apart from hypokalaemia such as high chlorine metabolic acidosis and hypercalcinuria. The genetic knockout or functional inhibition of Kir4.1 suppresses Na-Cl cotransporter (NCC) expression and activity in the DCT. However, the downregulation of Kir4.1 increases epithelial Na channel (ENaC) expression in the collecting duct. Recently, factors regulating expression and activity of Kir4.1 and Kir4.1/Kir5.1 were identified, such as cell acidification, dopamine, insulin and insulin-like growth factor-1. The involved mechanisms include PKC, PI3K, Src family protein tyrosine kinases and WNK-SPAK signal transduction pathways. Here we review the progress of renal tubule basolateral Kir, and mainly discuss the function and regulation of Kir4.1 and Kir4.1/Kir5.1.
Animals ; Cell Membrane ; Humans ; Kidney Tubules ; metabolism ; Kidney Tubules, Distal ; Membrane Potentials ; Mice ; Potassium Channels, Inwardly Rectifying ; metabolism

OBJECTIVETo investigate the expression and function of PKD1 and PKD2 in different kidney tissues and cell lines.

METHODSImmunoprecipitation, Western blotting, In situ hybridization and immunohistochemical staining methods were used to observe the expression of PKD1 mRNA and PKD2 mRNA and their protein abundance in different kidney tissues and cell lines.

RESULTSCoordinate expressions of PKD1 and PKD2 were found in all kidney tissues and cell lines. Distribution of PKD1 mRNA and PKD2 mRNA and their protein polycystin-1 and polycystin-2 in normal human adult kidney tissue were mainly expressed in the medullary collecting ducts and distal tubules. Positive staining was also found in the majority of cyst-lining epithelial cells of PKD1 cystic kidney tissue, PKD1 cyst-lining epithelia cell line and LLC-PK1. The expression level of them in cystic epithelia of ADPKD kidney tissue was much higher than that in adult renal tubules (P < 0.01).

CONCLUSIONSSimilar expression pattern of PKD1 and PKD2 and their different tissue distribution in different kidney tissues show that the molecular mutuality of PC-1 and PC-2 might be the base of their functional correlation. Polycystins might play an important role in the maintenance of tubular architecture.

Adult ; Animals ; Cell Line ; Gene Expression ; Humans ; Kidney ; metabolism ; Kidney Tubules, Collecting ; metabolism ; Kidney Tubules, Distal ; metabolism ; Kidney Tubules, Proximal ; cytology ; Polycystic Kidney, Autosomal Dominant ; pathology ; RNA, Messenger ; biosynthesis ; genetics ; Swine ; TRPP Cation Channels ; metabolism

Renal outer medullary potassium (ROMK) channel is an important K⁺ excretion channel in the body, and K⁺ secreted by the ROMK channels is most or all source of urinary potassium. Previous studies focused on the ROMK channels of thick ascending limb (TAL) and collecting duct (CD), while there were few studies on the involvement of ROMK channels of the late distal convoluted tubule (DCT2) in K⁺ excretion. The purpose of the present study was mainly to record the ROMK channels current in renal DCT2 and observe the effect of high potassium diet on the ROMK channels by using single channel and whole-cell patch-clamp techniques. The results showed that a small conductance channel current with a conductance of 39 pS could be recorded in the apical membrane of renal DCT2, and it could be blocked by Tertiapin-Q (TPNQ), a ROMK channel inhibitor. The high potassium diet significantly increased the probability of ROMK channel current occurrence in the apical membrane of renal DCT2, and enhanced the activity of ROMK channel, compared to normal potassium diet (P < 0.01). Western blot results also demonstrated that the high potassium diet significantly up-regulated the protein expression levels of ROMK channels and epithelial sodium channel (ENaC), and down-regulated the protein expression level of Na⁺-Cl^- cotransporter (NCC). Moreover, the high potassium diet significantly increased urinary potassium excretion. These results suggest that the high potassium diet may activate the ROMK channels in the apical membrane of renal DCT2 and increase the urinary potassium excretion by up-regulating the expression of renal ROMK channels.
Potassium Channels, Inwardly Rectifying/metabolism* ; Kidney Tubules, Distal/metabolism* ; Potassium/metabolism* ; Epithelial Sodium Channels/metabolism* ; Diet

OBJECTIVETo observe the expression of caspase-3 in the kidney of a rat model of renal tubular damage induced by endotoxin and hypoxia and explore the mechanism of renal tubular damage.

METHODSTen rats were anesthetized with artificial ventilation and received 2 mg/kg lipopolysaccharide (LPS) injection through the penile vein. The FiO2 was reduced 90 min later from 21% to 5%, and the ventilation was withdrawn after another 90 min. Immediately after ventilation withdrawal, the kidney of the rats were obtained for immunocytochemistry and HE staining.

RESULTSHE staining showed obvious hyperemia in most of the glomeruli, mild swelling of the endothelial and mesangial cells, severe swelling and turbidity in the proximal tubular epithelial cells without obvious changes in most of the distal proximal tubules. A small portion of the interstitial epithelial cells showed swelling and turbidity, and the entire renal interstitium appeared hyperemic but without inflammatory cell infiltration. Immunocytochemistry detected the presence of caspase-3 in the cytoplasm, and most of the distal renal tubule cells were positive for caspase-3, while only occasional cells showed caspase-3 positivity in the proximal tubular epithelial cells. Most of the proximal tubular epithelial and glomerulus cells were negative for caspase-3.

CONCLUSIONSEndotoxin and hypoxia can induce renal damage, particularly in the proximal renal tubule cells, and the distal tubular epithelial cells sustain relatively light damage. Caspase-3 is strongly expressed in the distal renal tubular cells, suggesting that in renal tubular damage induced by endotoxin and hypoxia, cell degeneration, necrosis and apoptosis coexist in the tubular epithelial cells; degeneration and necrosis occur primarily in the proximal tubular epithelial cells, while apoptosis is obvious in the distal renal cells.

Animals ; Caspase 3 ; genetics ; metabolism ; Hypoxia ; chemically induced ; Kidney ; metabolism ; Kidney Tubules ; metabolism ; pathology ; Lipopolysaccharides ; Male ; Rats ; Rats, Sprague-Dawley

This study was purposed to investigate the relationship between the catalysis of Bence Jones protein (BJP) in urine of patients with multiple myeloma(MM) and toxicity on the renal proximal tubular cells in vitro, and to explore the potential mechanism for the toxicity of BJP to renal impairment in patients with MM. The Michaelis-Menten constant (K(m)) and catalytic constant (k(cat)) of the amidase activity of BJP was calculated by Hanes equation. The LLC-PK1 cells were cultured with different concentration of BJP for 24 h, then proliferation of the cells were determined by MTT method and apoptosis were determined by flow cytometry. The results showed that the BJP from the MM patients with renal impairment significantly inhibited cell proliferation, as compared with that from MM patients without renal impairment. The BJP with higher k(cat) had higher toxicity to LLC-PK1 cells. BJP could induce apoptosis and necrosis of LLC-PK1 cells when reached a certain concentration and this effect enhanced with increase of BJP concentration. It is concluded that the catalysis of BJP and its toxicity to renal tubular epithelial cells has a positive correlation, and toxic effect of BJP on renal tubular epithelial cells results from inhibiting proliferation and inducing apoptosis and necrosis of the cells, which may be one of renal impairment mechanisms in MM patients.
Animals ; Bence Jones Protein ; metabolism ; toxicity ; Catalysis ; Coculture Techniques ; Epithelial Cells ; metabolism ; pathology ; Humans ; Kidney ; metabolism ; pathology ; Kidney Tubules ; cytology ; LLC-PK1 Cells ; Multiple Myeloma ; metabolism ; pathology ; Swine

Acute kidney injury is a serious global health problem and determinant of morbidity and mortality. Recent advancements in the field of stem cell research raise hopes for stem cell-based regenerative approaches to treat acute kidney diseases. In this review, the authors summarized the latest research advances of the adult resident renal progenitor cells (ARPCs) on kidney repair, the role of ARPCs on tubular regeneration after acute kidney injury, the current understanding of the mechanisms related to ARPC activation and modulation, as well as the challenges that remain to be faced.
Acute Kidney Injury ; physiopathology ; Antigens, CD ; metabolism ; Drugs, Chinese Herbal ; pharmacology ; Humans ; Kidney ; physiopathology ; Kidney Tubules ; physiopathology ; Receptors, CXCR ; metabolism ; Regeneration ; physiology ; Reperfusion Injury ; physiopathology ; Stem Cells ; physiology

An improved approach for determination of Na(+)-K(+)-ATPase activity in single proximal renal tubule of rat reported by Doucet and his colleagues has been suggested. The single proximal renal tubules were isolated by hand under stereomicroscope from collagenase II-treated renal cortical tissue in rats. The length of every single renal tubule segment obtained was measured. The single proximal renal tubules were treated with a hypoosmotic solution and with freeze-thaw successively, before incubation with [gamma-(32)P]-ATP. (32)Pi hydrolyzed from [gamma-(32)P]ATP by Na(+)-K(+)-ATPase in the single proximal renal tubules was assayed by liquid scintillation counting. The activity of Na(+)-K(+)-ATPase in the single proximal renal tubules was calculated by applying a modified formula. There was no significant difference in the measurement result of Na(+)-K(+)-ATPase activity between the method of Doucet et al. and the improved one, but the latter has advantage of less time, less reagents and being easy to operate.
Adenosine Triphosphate ; metabolism ; Animals ; Kidney Tubules, Proximal ; enzymology ; Male ; Microscopy ; Rats ; Rats, Wistar ; Sodium-Potassium-Exchanging ATPase ; metabolism ; Time Factors

Virtually all of the dietary potassium intake is absorbed in the intestine, over 90% of which is excreted by the kidneys regarded as the most important organ of potassium excretion in the body. The renal excretion of potassium results primarily from the secretion of potassium by the principal cells in the aldosterone-sensitive distal nephron (ASDN), which is coupled to the reabsorption of Na⁺ by the epithelial Na⁺ channel (ENaC) located at the apical membrane of principal cells. When Na⁺ is transferred from the lumen into the cell by ENaC, the negativity in the lumen is relatively increased. K⁺ efflux, H⁺ efflux, and Cl^- influx are the 3 pathways that respond to Na⁺ influx, that is, all these 3 pathways are coupled to Na⁺ influx. In general, Na⁺ influx is equal to the sum of K⁺ efflux, H⁺ efflux, and Cl^- influx. Therefore, any alteration in Na⁺ influx, H⁺ efflux, or Cl^- influx can affect K⁺ efflux, thereby affecting the renal K⁺ excretion. Firstly, Na⁺ influx is affected by the expression level of ENaC, which is mainly regulated by the aldosterone-mineralocorticoid receptor (MR) pathway. ENaC gain-of-function mutations (Liddle syndrome, also known as pseudohyperaldosteronism), MR gain-of-function mutations (Geller syndrome), increased aldosterone levels (primary/secondary hyperaldosteronism), and increased cortisol (Cushing syndrome) or deoxycorticosterone (hypercortisolism) which also activate MR, can lead to up-regulation of ENaC expression, and increased Na⁺ reabsorption, K⁺ excretion, as well as H⁺ excretion, clinically manifested as hypertension, hypokalemia and alkalosis. Conversely, ENaC inactivating mutations (pseudohypoaldosteronism type 1b), MR inactivating mutations (pseudohypoaldosteronism type 1a), or decreased aldosterone levels (hypoaldosteronism) can cause decreased reabsorption of Na⁺ and decreased excretion of both K⁺ and H⁺, clinically manifested as hypotension, hyperkalemia, and acidosis. The ENaC inhibitors amiloride and Triamterene can cause manifestations resembling pseudohypoaldosteronism type 1b; MR antagonist spironolactone causes manifestations similar to pseudohypoaldosteronism type 1a. Secondly, Na⁺ influx is regulated by the distal delivery of water and sodium. Therefore, when loss-of-function mutations in Na⁺-K⁺-2Cl^- cotransporter (NKCC) expressed in the thick ascending limb of the loop and in Na⁺-Cl^- cotransporter (NCC) expressed in the distal convoluted tubule (Bartter syndrome and Gitelman syndrome, respectively) occur, the distal delivery of water and sodium increases, followed by an increase in the reabsorption of Na⁺ by ENaC at the collecting duct, as well as increased excretion of K⁺ and H⁺, clinically manifested as hypokalemia and alkalosis. Loop diuretics acting as NKCC inhibitors and thiazide diuretics acting as NCC inhibitors can cause manifestations resembling Bartter syndrome and Gitelman syndrome, respectively. Conversely, when the distal delivery of water and sodium is reduced (e.g., Gordon syndrome, also known as pseudohypoaldosteronism type 2), it is manifested as hypertension, hyperkalemia, and acidosis. Finally, when the distal delivery of non-chloride anions increases (e.g., proximal renal tubular acidosis and congenital chloride-losing diarrhea), the influx of Cl^- in the collecting duct decreases; or when the excretion of hydrogen ions by collecting duct intercalated cells is impaired (e.g., distal renal tubular acidosis), the efflux of H⁺ decreases. Both above conditions can lead to increased K⁺ secretion and hypokalemia. In this review, we focus on the regulatory mechanisms of renal potassium excretion and the corresponding diseases arising from dysregulation.
Humans ; Bartter Syndrome/metabolism* ; Pseudohypoaldosteronism/metabolism* ; Potassium/metabolism* ; Aldosterone/metabolism* ; Hypokalemia/metabolism* ; Gitelman Syndrome/metabolism* ; Hyperkalemia/metabolism* ; Clinical Relevance ; Epithelial Sodium Channels/metabolism* ; Kidney Tubules, Distal/metabolism* ; Sodium/metabolism* ; Hypertension ; Alkalosis/metabolism* ; Water/metabolism* ; Kidney/metabolism*

The purpose of this study was to determine the expression and distribution of band 3 in the collecting duct and connecting tubules of the kidney of the marmoset monkey (Callithrix jacchus), and to establish whether band 3 is expressed in type A intercalated cells. The intracellular localization of band 3 in the different populations of intercalated cells was determined by double-labeling immunohistochemistry. Immunohistochemical microscopy demonstrated that band 3 is located in the basolateral plasma membranes of all type A intercalated cells in the connecting tubule (CNT), cortical collecting duct (CCD), and outer medullary collecting duct (OMCD) of the marmoset. However, type B intercalated cells and non-A/ non-B intercalated cells did not show band 3 labeling. Electron microscopy of the CNT, CCD and OMCD confirmed the light microscopic observation of the basolateral plasma membrane staining for band 3 in a subpopulation of interacted cells. Basolateral staining was seen on the plasma membrane and small coated vesicles in the perinuclear structure, some of which were located in the Golgi region. In addition, there was no labeling of band 3 in the mitochondria of the CNT, CCD and in OMCD cells. The intensity of the immunostaining of the basolateral membrane was less in the CNT than in the CCD and OMCD. In contrast, band 3 immunoreactivity was greater in the intracellular vesicles of the CNT. From these results, we suggest that the basolateral Cl-/HCO3- exchanger in the monkey kidney is in a more active state in the collecting duct than in the CNT.
Animals ; Anion Exchange Protein 1, Erythrocyte/*metabolism ; Callithrix/*metabolism ; Gene Expression Profiling/veterinary ; *Gene Expression Regulation ; Immunohistochemistry/veterinary ; Kidney Tubules/cytology/physiology/ultrastructure ; Kidney Tubules, Collecting/cytology/*metabolism/ultrastructure ; Male ; Microscopy, Electron, Transmission/veterinary