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*

In end-stage renal disease (ESRD) patients regardless of dialysis modes, i.e. maintenance hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD), potassium (K) homeostasis is regulated primarily via dialysis and extrarenal K regulation in the diverse daily K intake. However, K metabolism has been known to differ greatly between the two main methods of dialysis. Hyperkalemia is a common complication (10-24%) and the most common cause of the death (3-5%) among electrolyte disorders in patients on maintenance HD. On the contrary, hypokalemia (10-36%) is responsible for a rather common complication and independent prognostic factor on CAPD. Although excessive K intake or inadequate dialysis on maintenance HD and poor nutritional K intake on CAPD are accused without doubts upto 50% of ESRD patients as a primary cause of the K-imbalance, i.e. hyperkalemia on HD and hypokalemia on CAPD, other contributory factors including certain medications and unknown causes remain still to be resolved. Accordingly, the effects of medications as another source of K-imbalance on HD with RAS blockades and beta blockers as well as those of conventional and glucose-free dialysates (Icodextrin) for internal K-redistribution on CAPD were evaluated with reviewing the literatures and our data. Furthermore, new developments in the clinical managements of hyperkalemia on HD following the exclusion of pseudohyperkalemia before the initiation of dialysis were suggested, especially, by the comparison of the effects between mono- and dual-therapy with medications for transcellular K shifting in the emergent situation. Also, the intraperitoneal K administration via conventional glucose-containing (2.5%) and glucose-free dialysates (Icodextrin) as a specific route of K-supplementation for hypokalemia on CAPD was examined for its efficiency and the degree of intracellular K shift between these two different types of dialysates.
Dialysis ; Dialysis Solutions ; Homeostasis ; Humans ; Hyperkalemia ; Hypokalemia ; Kidney Failure, Chronic ; Metabolism ; Peritoneal Dialysis, Continuous Ambulatory* ; Potassium ; Renal Dialysis*

Cyclosporin A (CsA)-induced hyperkalemia is caused by alterations in transepithelial K(+) secretion resulting from the inhibition of renal tubular Na(+), K(+) -ATPase activity. Thyroxine enhances renal cortical Na(+), K(+) -ATPase activity. This study investigated the effect of thyroxine on CsA-induced hyperkalemia. Sprague-Dawley rats were treated with either CsA, thyroxine, CsA and thyroxine, or olive-oil vehicle. CsA resulted in an increase in BUN and serum K(+), along with a decrease in creatinine clearance, fractional excretion of potassium, and renal cortical Na(+), K(+) -ATPase activity, as compared with oil vehicle administration. Histochemical study showed reduced Na(+), K(+) -ATPase activity in the proximal tubular epithelial cells of the CsA-treated compared with the oil-treated rats. Histologically, isometric intracytoplasmic vacuolation, disruption of the arrangement and swelling of the mitochondria, and a large number of lysosomes in the tubular epithelium were characteristic of the CsA-treated rats. Co-administration of thyroxine prevented CsA-induced hyperkalemia and reduced creatinine clearance, Na(+), K(+) -ATPase activity, and severity of the histologic changes in the renal tubular cells when compared with the CsA-treated rats. Thyroxine increased the fractional excretion of potassium via the preservation of Na(+), K(+) -ATPase activity in the renal tubular cells. Thus, the beneficial effects of thyroxine may be suited to treatment modalities for CsA-induced hyperkalemia.
Animals ; Cyclosporine/antagonists & inhibitors/*toxicity ; Hyperkalemia/chemically induced/*drug therapy/metabolism/prevention & control ; Immunosuppressive Agents/antagonists & inhibitors/*toxicity ; Kidney Cortex/*drug effects/*enzymology/pathology ; Male ; Microsomes/enzymology ; Potassium/blood/metabolism ; Rats ; Rats, Sprague-Dawley ; Sodium-Potassium-Exchanging ATPase/*metabolism ; Thyroxine/*pharmacology

WNKs (with-no-lysine [K]) are a family of serine-threonine protein kinases with an atypical placement of the catalytic lysine relative to all other protein kinases. The roles of WNK kinases in regulating ion transport were first revealed by the findings that mutations of two members cause a genetic hypertension and hyperkalemia syndrome. More recent studies suggest that WNKs are pleiotropic protein kinases with important roles in many cell processes in addition to ion transport. Here, we review roles of WNK kinases in the regulation of ion balance, cell signaling, survival, and proliferation, and embryonic organ development.
Amino Acid Sequence ; Animals ; Cell Proliferation ; Cell Survival ; Humans ; Hyperkalemia/enzymology/etiology/genetics ; Hypertension/enzymology/etiology/genetics ; Kidney/enzymology ; Models, Molecular ; Molecular Sequence Data ; Mutation ; Neoplasms/enzymology/etiology/genetics ; Protein Structure, Tertiary ; Protein-Serine-Threonine Kinases/*chemistry/genetics/*metabolism ; Pseudohypoaldosteronism/enzymology/etiology/genetics ; Sequence Homology, Amino Acid ; Signal Transduction ; Syndrome

Acute renal failure refers to a rapid reduction in renal function that usually occurs in an individual with no known previous renal disease. Development of a complication of acue renal failure in critically ill surgical patients is not unusual, and it causes high morbidity and mortality. Acute renal failure can be divided as Pre-renal (functional), Renal (organic), and Postrenal (obstructive) azotemia according to their etiologies. Early recognition and proper correction of pre-renal conditions are utter most important to prevent an organic damage of kidney. These measures include correction of dehydration, treatment of sepsis, and institution of shock therapy. Prolonged exposure to ischemia or nephrotoxin may lead a kidney to permanent parenchymal damage. A differential diagnosis between functional and organic acute renal failure may not be simple in many clinical settings. Renal functional parameters, such as FENa+ or renal failure index, are may be of help in these situations for the differential diagnosis. Provocative test utilizing mannitol, loop diuretics and renovascular dilators after restoration of renal circulation will give further benefits for diagnosis or for prevention of functional failure from leading to organic renal failure. Converting enzyme blocker, dopamine, calcium channel blocker, and propranolol are also reported to have some degree of renal protection from bioenergetic renal insults. Once diagnosis of acute tubular necrosis has been made, all measures should be utilized to maintain the patient until renal tubular regeneration occurs. Careful regulation of fluid, electrolyte, and acid-base balance is primary goal. Hyperkalemia over 6.5 mEq/l is a medical emergency and it should be corrected immediately. Various dosing schedules for medicines excreting through kidney have been suggested but none was proved safe and accurate. Therefore blood level of specific medicines better be checked before each dose, especially digoxin and Aminoglycosides. Indication for application of ultrafiltration hemofilter or dialysis may be made by individual base.
Acid-Base Equilibrium ; Acute Kidney Injury* ; Aminoglycosides ; Appointments and Schedules ; Azotemia ; Calcium Channels ; Convulsive Therapy ; Critical Illness ; Dehydration ; Diagnosis* ; Diagnosis, Differential ; Dialysis ; Digoxin ; Dopamine ; Emergencies ; Energy Metabolism ; Humans ; Hyperkalemia ; Ischemia ; Kidney ; Mannitol ; Mortality ; Necrosis ; Propranolol ; Regeneration ; Renal Circulation ; Renal Insufficiency ; Sepsis ; Sodium Potassium Chloride Symporter Inhibitors ; Ultrafiltration