title: Fluid movements across rabbit ileum coupled to passive paracellular ion movements.
abstract: 1. Theophylline (10 mM) and choleragen (1 x 10(-6) g ml.-1) abolish net fluid absorption by everted sacs of rabbit ileum. Triaminopyrimidine (20 mM) and ethacrynate (0.1 mM) prevent this inhibition of net fluid movement. Replacing Ringer Cl- with isethionate prevents the theophylline-dependent decrease in fluid absorption also. 2. Ouabain (0.1 mM) abolishes net fluid movements in both control and theophylline-treated tissue. 3. With ouabain present, hypertonic NaCl (200 mM) in the mucosal solution causes net fluid secretion (serosal-mucosal flux). With theophylline added to both the mucosal and serosal solution, net fluid absorption (mucosal-serosal flux) is observed (P less than 0.001). Triaminopyrimidine (20 mM), or ethacrynate (0.1 mM), or replacement of Ringer Na+ with choline, or Ringer Cl- with isethionate all prevent the theophylline-induced reversal of osmotic flow. 4. Theophylline increases passive net flux of Na+ and Cl- from mucosal solution containing hypertonic (200 mM) NaCl+ ouabain (0.1 mM) across sheets of ileum into serosal solution containing mannitol Ringer + ouabain. The increased passive Na+ flux is blocked by triaminopyrimidine and the increased Na+ and Cl- fluxes are blocked by ethacrynate (0.1 mM). 5. The suggested route of increased NaCl leakage is via the paracellular pathway as it is inhibited by triaminopyrimidine. The increase, itself, is a consequence of the increased passive permeability of the mucosal border to Cl-, induced by theophylline or choleragen. Water is apparently electro-osmotically coupled to the paracellular Na+ leakage (100 mole water mole-1 Na+), hence increased passive leakage reverses osmotic flow. In active tissue the lateral intercellular space contains hypertonic NaCl, and hence increased leakage of NaCl across the tight-junction in theophylline or choleragen-treated tissue gives rise to net fluid secretion.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism*; D002772:Cholera Toxin / Q000494:pharmacology; D004976:Ethacrynic Acid / Q000494:pharmacology; D007082:Ileum / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000378:metabolism; D007419:Intestinal Secretions / Q000502:physiology*; D008353:Mannitol / Q000494:pharmacology; D009995:Osmosis; D010042:Ouabain / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D011817:Rabbits; D012462:Saline Solution, Hypertonic; D012636:Secretory Rate / Q000187:drug effects; D012704:Serous Membrane / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D013806:Theophylline / Q000494:pharmacology
chemical_list: D002712:Chlorides; D011743:Pyrimidines; D012462:Saline Solution, Hypertonic; D008353:Mannitol; D010042:Ouabain; D002772:Cholera Toxin; D012964:Sodium; D013806:Theophylline; D004976:Ethacrynic Acid