[Regulation of kidney on potassium balance and its clinical significance].

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.