Physiological concentrations of bile salts inhibit recovery of ischemic-injured porcine ileum

We have previously shown rapid in vitro recovery of barrier function in porcine ischemic-injured ileal mucosa, attributable principally to reductions in paracellular permeability. However, these experiments did not take into account the effects of luminal contents, such as bile salts. Therefore, the objective of this study was to evaluate the role of physiological concentrations of deoxycholic acid in recovery of mucosal barrier function. Porcine ileum was subjected to 45 min of ischemia, after which mucosa was mounted in Ussing chambers and exposed to varying concentrations of deoxycholic acid. The ischemic episode resulted in significant reductions in transepithelial electrical resistance (TER), which recovered to control levels of TER within 120 min, associated with significant reductions in mucosal-to-serosal ³H-labeled mannitol flux. However, treatment of ischemic-injured tissues with 10-5 M deoxycholic acid significantly inhibited recovery of TER with significant increases in mucosal-to-serosal ³H-labeled mannitol flux, whereas 10^-6 M deoxycholic acid had no effect. Histological evaluation at 120 min revealed complete restitution regardless of treatment, indicating that the breakdown in barrier function was due to changes in paracellular permeability. Similar effects were noted with the application of 10^-5 M taurodeoxycholic acid, and the effects of deoxycholic acid were reversed with application of the Ca²⁺-mobilizing agent thapsigargin. Deoxycholic acid at physiological concentrations significantly impairs recovery of epithelial barrier function by an effect on paracellular pathways, and these effects appear to be Ca²⁺-dependent.