title: Consequences of potassium recycling in the renal medulla. Effects of ion transport by the medullary thick ascending limb of Henle's loop.
abstract: The consequences of K recycling and accumulation in the renal medulla were examined by measuring the effect of elevated K concentration on ion transport by the medullary thick ascending limb of Henle's loop. Perfused and bathed in vitro, thick limbs from both mouse and rabbit displayed a graded, reversible reduction of transepithelial voltage after increasing K concentration from 5 to 10, 15, or 25 mM. The effect was reproducible whether osmolality was 328 or 445 mosmol/kg H2O, and whether K replaced Na or choline. Net chloride absorption and transepithelial voltage were reduced by almost 90% when ambient K concentration was 25 mM. When either lumen or bath K was increased to 25 mM, net Na absorption was reduced. There was spontaneous net K absorption when perfusate and bath K concentration was 5 mM. Analysis of transepithelial K transfer after imposition of chemical gradients demonstrated rectification in the absorptive direction. Absorption of K by this segment provides a means to maintain high medullary interstitial concentration. Accumulation of K in the outer medulla, by reducing NaCl absorption, would increase volume flow through the loop of Henle and increase Na and water delivery to the distal nephron. K recycling thus might provide optimum conditions for K secretion by the distal nephron.
mesh_terms: D000042:Absorption; D000818:Animals; D005260:Female; D007473:Ion Channels / Q000378:metabolism*; D007679:Kidney Medulla / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism*; D008138:Loop of Henle / Q000378:metabolism*; D008433:Mathematics; D051379:Mice; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D013997:Time Factors
chemical_list: D007473:Ion Channels; D011188:Potassium