Fluid movements across rabbit ileum coupled to passive paracellular ion movements.

Abstract

SUMMARY1. Theophylline (10 mM) and choleragen (1 x 10-6 g ml.-') abolish net fluid absorption by everted sacs of rabbit ileum. Triaminopyrimidine (20 mm) and ethacrynate (0X1 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. 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-' 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 choieragen-treated tissue gives rise to net fluid secretion.

Electrophysiological and electron‐microscopical correlations with fluid and electrolyte secretion in rabbit ileum.

“…The mannitol dilution potential was also measured across unstripped rabbit ileum in incubation conditions identical to those described in Holman & Naftalin (1979), i.e. 200 mM-NaCl Ringer+ 0 1 mM-ouabain in the mucosal solution and isotonic mannitol Ringer+ +0 mM-ouabain in the serosal solution.…”

“…In this series of experiments the tissue was incubated in identical conditions to those described in the previous paper (Holman & Naftalin, 1979), i.e. 200 mM-NaCl Ringer in the mucosal solution, isotonic NaCl Ringer in the serosal solution, 0-1 mM-G. D. HOLMAN AND OTHERS ouabain present in both solutions; when present, triaminopyrimidine and theophylline were at 20 and 10 mm respectively in both solutions.…”

“…In the preceding paper passive negative osmosis across rabbit ileum treated either with choleragen, or with theophylline is described; it is also shown that this effect appears to depend on increased circulation of current due to coupled downhill NaCl movements (Holman & Naftalin, 1979). Powell (1974) has demonstrated that the relative permeability of Cl: Na is changed from 047 to 0-68 by theophylline, or choleragen in ouabain-poisoned rabbit ileum.…”

Reversal and inhibition of cholera toxin‐induced secretion in isolated rabbit ileum.

“…The effect of cholera toxin on ileal sacs is not observed until about 90 min incubation time has elapsed (Holman & Naftalin, 1979). This time lag is due to time-dependent processes involved in the binding of toxin B subunits to membrane receptors, followed by insertion of toxin A subunits into cells.…”

“…This toxin penetrates cells more rapidly than cholera toxin, but no significant difference was found between mean AW values at 60 min incubation. A similar experiment was performed using theophylline, but data were analysed and plotted from 30 min incubation since this acts more quickly (Holman & Naftalin, 1979). In addition, an attempt was made to reverse theophylline-induced secretion after 135 min incubation with nicotinamide.…”