title: Ion transport by rabbit descending colon: mechanisms of transepithelial potassium transport.
abstract: In vitro preparations of rabbit descending colon were studied under steady-state short-circuit conditions to determine 1) the K concentration dependence of unidirectional K fluxes; 2) the effects of the K channel blocker barium and the diuretic agent furosemide; and 3) the steady-state tissue specific activity of 42K when added to the luminal bathing solution. Results from these studies reveal that 1) labeling of cellular K from the mucosal solution is less than 25% of that from the serosal solution; 2) both unidirectional K fluxes are composed of saturable and nonsaturable components; 3) the serosal-to-mucosal saturable component is abolished by ouabain, and subsequent addition of 2,4-dinitrophenol abolishes the saturable component of the mucosal-to-serosal K flux; 4) luminal or serosal barium alters K transport in a manner consistent with the presence of barium-sensitive K conductances at both membranes; 5) luminal furosemide did not alter K transport; and 6) there is no shunt selectivity for K. We conclude that the majority of both unidirectional K fluxes follow a transcellular pathway and that both the apical and basolateral membranes possess active K uptake mechanisms and barium-sensitive K exit mechanisms.
mesh_terms: D019297:2,4-Dinitrophenol; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D003106:Colon / Q000187:drug effects / Q000502:physiology*; D004140:Dinitrophenols / Q000494:pharmacology; D004848:Epithelium / Q000378:metabolism; D005665:Furosemide / Q000494:pharmacology; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits
chemical_list: D004140:Dinitrophenols; D001464:Barium; D010042:Ouabain; D005665:Furosemide; D019297:2,4-Dinitrophenol; D011188:Potassium