title: Cellular K+ permeation across the cortical collecting tubule: effects of Na+-K+ pump inhibition and membrane depolarization.
abstract: These experiments examined the possibility that alterations in cell cation content and/or membrane voltage could influence cell K+ permeability of the cortical collecting tubule. Using the amiloride-treated isolated perfused rabbit cortical collecting tubule, ouabain or a K+-free bath reduced the magnitude of the K+ diffusion voltage. In addition, both methods of Na+-K+-ATPase inhibition reduced the K+ efflux (lumen-to-bath) rate coefficient (KK) without affecting the Na+ efflux rate coefficient. The magnitude of the reduction of KK could not be explained by a model of simple diffusion across two membranes in series even if the intracellular voltage were abolished. Thus, pump inhibition reduced cell K+ permeability. To determine whether membrane depolarization could induce a change in membrane permeability, [K+] was increased to 20 mM in both perfusate and bath. The reduction in KK was within the range predicted by the three-compartment model (36%). Differential membrane depolarization by raising lumen [K+] or bath [K+] produced disparate results. Apical depolarization reduced KK but basolateral depolarization did not. Taken together these results indicate that intracellular ion content may play a major role in regulating cell K+ permeability independent of voltage-dependent effects. In addition, under these experimental conditions, the apical membrane may be the rate-limiting barrier to cellular transfer.
mesh_terms: D000818:Animals; D007684:Kidney Tubules / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials; D010042:Ouabain / Q000494:pharmacology; D010539:Permeability; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors
chemical_list: D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium