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

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 vectorial transepithelial transport of water and electrolytes in the renal epithelium is achieved by the polarized distribution of various transport proteins in the apical and basolateral membrane. The short-term regulation of transepithelial transport has been traditionally thought to be mediated by kinetic alterations of transporter without changing the number of transporters. However, a growing body of recent evidence supports the possibility that the stimulus-dependent recycling of transporter-carrying vesicles can alter the abundance of transporters in the plasma membrane in parallel changes in transepithelial transport functions. The abundance of transporters in the plasma membrane is determined by net balance between stimulus-dependent exocytic insertion of transporters into and endocytic retrieval of them from the plasma membrane. The vesicular recycling occurs along the tracts of the actin microfilaments and microtubules with associated motors. This review is to highlight the importance of vesicular transport in the short-term regulatory process of transepithelial transport in the renal epithelium. In the short-term regulation of many other renal transporters, vesicular transport is likely to be also involved. Thus, vesicular transport is now emerged as a wide-spread general regulatory mechanism involved in short-term regulation of renal functions.
Animal ; Biological Transport/physiology ; Endocytosis/physiology* ; Epithelial Cells/enzymology* ; Epithelial Cells/cytology* ; Exocytosis/physiol(HCMV)* ; H(+)-Transporting ATP Synthase/metabolism* ; Human ; Sodium Channels/metabolism

Adaptation, Physiological ; Animals ; Biological Transport ; Epithelial Sodium Channels ; physiology ; Extravascular Lung Water ; metabolism ; Fetus ; metabolism ; Humans ; Infant, Newborn ; Lung ; metabolism ; Pulmonary Surfactants ; metabolism

OBJECTIVETo investigate the epithelial sodium channel (ENaC) subunit mRNA expression in acutely isolated rat alveolar type II (ATII) cells.

METHODSAcutely isolated ATII cells from 20 SD rats were purified and ENaC alpha, beta, gamma-subunit mRNA levels were determined by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTSmRNA expressions of all the subunits were detected in the ATII cells, and ENaC alpha-subunit mRNA showed significantly higher expression than beta- and gamma-subunit mRNAs, and the expressions of the latter two mRNAs were comparable.

CONCLUSIONAs the predominant ENaC subunit expressed at the mRNA level in rat ATII cells, the alpha-subunit of ENAC plays an important role in alveolar fluid clearance.

Animals ; Cells, Cultured ; Epithelial Sodium Channels ; genetics ; metabolism ; Male ; Pulmonary Alveoli ; cytology ; metabolism ; RNA, Messenger ; genetics ; metabolism ; Rats ; Rats, Sprague-Dawley

OBJECTIVETo study the effect of aldosterone on aquaporin and ionophorous protein expressions in the cochlea of guinea pigs.

METHODSRT-PCR was used to detect the expression of Na-K ATPase and epithelial sodium channel (ENaC) mRNA in the cochlea of guinea pigs 6 h after intraperitoneal aldosterone injection. Immunohistochemistry was used to detect the expression of aquaporin 1(AQP1) in the cochlea 1 month after the injection.

RESULTSEarly after aldosterone injection, the expression level of Na-K ATPase beta(1) and beta(3) subunit mRNAs remained unchanged and level of ENaC alpha subunit mRNA was up-regulated in the cochlear lateral wall (P<0.05), and 1 month after the injection, the expression of AQP1 protein was down-regulated (P<0.05).

CONCLUSIONThe effect of aldosterone on the cochlea is mediated possibly through its action on the genome, and aldosterone may cause ion concentration alterations to induce endolymphatic hydrops.

Aldosterone ; pharmacology ; Animals ; Aquaporin 1 ; metabolism ; Cochlea ; drug effects ; metabolism ; Epithelial Sodium Channels ; metabolism ; Guinea Pigs ; Immunohistochemistry ; RNA, Messenger ; metabolism ; Reverse Transcriptase Polymerase Chain Reaction ; Sodium-Potassium-Exchanging ATPase ; metabolism ; Up-Regulation

OBJECTIVETo investigate the effect of arginine vasopressin (AVP) on alveolar fluid clearance (AFC) in acute lung injury (ALI).

METHODSForty-eight healthy adult Sprague-Dawley rats were randomly divided into control group, ALI model group and AVP treatment group. The pathological changes in the lungs, lung water content, alveolar permeability and AFC were observed, and the expressions of alveolar epithelial sodium channel (ENaC) and Na⁺, K⁺-ATPase were measured.

RESULTSCompared with those in the model group, the rats treated with AVP showed significantly decreased alveolar permeability (0.27 ± 0.15 vs 0.59 ± 0.19) and lung water content (5.01 ± 1.59 vs 8.67 ± 1.79) (P<0.05) and increased AFC (23.56 ± 4.51 vs 8.28 ± 3.57) and of α-ENaC expressions (1.296 ± 0.322 vs 0.349 ± 0.141) and α1-Na⁺, K⁺-ATPase (1.421 ± 0.389 vs 0.338 ± 0.186) (P<0.05).

CONCLUSIONAVP can promote AFC in with ALI possibly by up-regulation of α-ENaC, α1-Na⁺, and K⁺-ATPase.

Acute Lung Injury ; drug therapy ; Animals ; Arginine Vasopressin ; pharmacology ; Epithelial Sodium Channels ; metabolism ; Lung ; drug effects ; pathology ; Pulmonary Alveoli ; drug effects ; physiopathology ; Rats ; Rats, Sprague-Dawley ; Sodium-Potassium-Exchanging ATPase ; metabolism

OBJECTIVETo investigate the role of interleukin-17 (IL-17) in alveolar fluid clearance in mice with acute lung injury (ALI) and explore the possible mechanism.

METHODSSixteen IL-17-knockout mice and 16 wild-type mice were both randomized for intratracheal instillation of PBS (control) on lipopolysaccharide (LPS) to induce ALI. Forty-eight hours after the treatments, the wet-dry ratio (W/D) of the lungs, IL-8 in the bronchoalveolar lavage fluid (BALF) and histopathological changes of the lung tissues were examined. The expressions of epithelial sodium channel α subunit (α-ENaC) was detected with Western blotting and liver kinase B1 (LKB1) was detected with immunohistochemistry.

RESULTSCompared with wild-type mice treated with LPS, IL-17 knockout mice showed significantly decreased W/D of the lungs (9.739∓3.3 vs 5.351∓0.56) and IL-8 level in the BALF (67.50∓7.33 vs 41.00∓3.16 pg/mL) following LPS challenge. Pathological examination revealed reduced alveolar edema fluid aggregations and lower lung injury score in IL-17 knockout mice with also higher expression levels of ENaC and LKB1 compared with the wild-type mice.

CONCLUSIONKnocking out IL-17 in mice not only alleviates inflammation of the lung tissue following ALI but also reduces the loss of ENaC protein and promotes alveolar fluid clearance, mechanism of which is probably associated with LKB1.

Acute Lung Injury ; metabolism ; Animals ; Bronchoalveolar Lavage Fluid ; chemistry ; Epithelial Sodium Channels ; metabolism ; Gene Knockout Techniques ; Interleukin-17 ; genetics ; metabolism ; Interleukin-8 ; metabolism ; Lipopolysaccharides ; Lung ; pathology ; Mice ; Protein-Serine-Threonine Kinases ; metabolism

OBJECTIVETo study the effects of sodium on rat osteoblast function and explore the role of epithelial sodium channel (ENaC) in such effects.

METHODSThe proliferation and differentiation of rat osteoblasts were evaluated following treatment with 1×10(-4) mol/L to 1 mol/L Na(+). The mRNA expressions of the osteogenic genes and ENaC-α gene in the treated cells were assessed using RT-PCR.

RESULTSWithin the concentration of 1×10(-4) mol/L to 1 mol/L, Na(+) showed a two-way effect on the osteoblasts: low-concentration Na(+) (1×10(-4) mol/L) significantly promoted osteoblast differen- tiation, while at higher concentrations (0.5 and 1 mol/L), Na(+) produced an opposite effect. Sodium did not significantly affect osteoblast proliferation. Low-concentration Na(+) significantly increased the transcription of Cbfa1, OPN and OC, while high concentrations of Na(+) decreased their transcription. Low-concentration Na(+) also enhanced the mRNA expression of ENaC-α, but high-concentration Na(+) treatment lowered ENaC-α mRNA expression.

CONCLUSIONNa(+) displays a direct dose-related effect on osteoblasts by affecting its differentiation, osteogenic gene expression profile, and ENaC-α gene expression, suggesting the involvement of ENaC in Na(+)-mediated functional modulation of rat osteoblasts.

Animals ; Animals, Newborn ; Cell Differentiation ; drug effects ; Cell Proliferation ; drug effects ; Cells, Cultured ; Epithelial Sodium Channels ; metabolism ; Osteoblasts ; cytology ; drug effects ; Rats ; Rats, Sprague-Dawley ; Sodium Chloride ; pharmacology ; Transcriptome

OBJECTIVETo explore the role of epithelial sodium channel (ENaC) in regulating the functional activity of osteoclasts.

METHODSMultinucleated osteoclasts were obtained by inducing the differentiation of rat bone marrow cells with macrophage colony-stimulating factor (M-CSF) and RANKL. The osteoclasts were exposed to different concentrations of the ENaC inhibitor amiloride, and the expression of ENaC on osteoclasts was examined using immunofluorescence technique. The osteoclasts were identified with tartrate-resistant acid phosphatase (TRAP) staining, and the positive cells were incubated with fresh bovine femoral bone slices and the number of bone absorption pits was counted by computer-aided image processing. RT-PCR was performed to analyze the expression of cathepsin K in the osteoclasts.

RESULTSs Exposure to different concentrations of amiloride significantly inhibited the expression of ENaC and reduced the number of TRAP-positive osteoclasts. Exposure of the osteoclasts to amiloride also reduced the number of bone resorption pits on bone slices and the expression of osteoclast-specific gene cathepsin K.

CONCLUSIONs ENaC may participate in the regulation of osteoclast differentiation and bone resorption, suggesting its role in functional regulation of the osteoclasts and a possibly new signaling pathway related with ENaC regulation for modulating bone metabolism.

Animals ; Bone Marrow Cells ; cytology ; Bone Resorption ; Cathepsin K ; metabolism ; Cattle ; Cell Differentiation ; Epithelial Sodium Channels ; metabolism ; Macrophage Colony-Stimulating Factor ; metabolism ; Osteoclasts ; cytology ; RANK Ligand ; metabolism ; Rats ; Signal Transduction