title: Disposition and regulation of body potassium: an overview.
abstract: Most of filtered K+ is reabsorbed passively in the proximal tubule since the tubular fluid (TF): plasma (P) concentration ratio is almost identical to the equilibrium value calculated from the transtubular potential difference. In the loop of Henle, K+ also moves passively along chemical and electrical gradients. Only 5-10% of the filtered K+ remains in the early distal convoluted tubule. In the distal convoluted tubule TF/P K+ is lower than the calculated equilibrium value suggesting that K+ is passively secreted and actively reabsorbed. Most of the excreted K+ had been secreted by the end of the distal convoluted tubule. Aldosterone increases K+ secretion in this segment, an effect that may be dissociated from the effect on Na+. The relation between K+ secretion and Na+ absorption is the consequence of the luminal electronegativity produced by Na+ absorption and is not stoichiometric. Acidosis and alkalosis decrease and increase K+ secretion in the distal tubule respectively; this is not due to reciprocal changes in H+ secretion. Normally, some K+ is reabsorbed in the collecting duct. During K+ deprivation and loading the collecting duct may participate in the conservation or elimination of K+ respectively. Adaptation to chronic K+-loading consists of renal and extrarenal factors. The extrarenal mechanism is aldosterone-dependent and consists of rapid uptake of K+ by muscle. The renal mechanism consists of increased K+ secretion by the distal tubule. Luminal electronegativity and increased K+ pool in the distal tubular cell play a crucial role.
mesh_terms: D000136:Acid-Base Equilibrium / Q000187:drug effects; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects; D005110:Extracellular Space / Q000378:metabolism; D005919:Glomerular Filtration Rate; D006801:Humans; D006947:Hyperkalemia / Q000378:metabolism; D007010:Hyponatremia / Q000378:metabolism; D007668:Kidney / Q000201:enzymology; D007686:Kidney Tubules, Distal / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008138:Loop of Henle / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008901:Mineralocorticoids / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism
chemical_list: D008901:Mineralocorticoids; D012964:Sodium; D000251:Adenosine Triphosphatases; D011188:Potassium