Prostaglandin-Mediated Inhibition of the Na⁺/H⁺ Exchanger Isoform 2 Stimulates Recovery of Barrier Function in Ischemia-Injured Intestine - Prostaglandins stimulate repair of the ischemia- injured intestinal barrier inn porcine ileum through a mechanism involving cAMPdependent Cl^- secretion and inhibition of electroneutral Na⁺/H⁺ exchange (NHE) activity. In the present study, we focused on the role of individual NHE isoforms in the recovery of barrier function. Ischemia- injured porcine ileal mucosa was mounted on Ussing chambers. Short circuit current (I_SC), transepithelial electrical resistance (TER), and isotopic fluxes of ²²Na were measured in response to prostaglandin E₂ (PGE₂) and selective inhibitors of epithelial NHE isoforms. Immunoassays were used to assess the expression of NHE isoforms. Forty-five minutes of intestinal ischemia resulted in a 45% reduction in TER (P<0.01). Near-complete restitution occurred within 60-minutes. Inhibition of the NHE isoform 2 (NHE2) with HOE-694 (25 µM) added to the mucosal surface of injured ileum, stimulated significant elevations in TER independent of changes in I_SC and histologic evidence of restitution. Pharmacologic inhibition of NHE3 or NHE1 with mucosal S3226 (20 µM) or serosal cariporide (25 mM), respectively, had no effect. Ischemia-injured tissues treated with mucosal S3226 or HOE-694 exhibited equivalent reductions in mucosal-to-serosal fluxes of ²²Na⁺ (by ~ 35%) compared with non-treated ischemia- injured control tissues (P<0.05). Intestinal ischemia resulted in increased expression of the cytoplasmic NHE regulatory factor EBP50 in NHE2, but not in NHE3 immunoprecipitates. Selective inhibition of NHE2, and not NHE3, induces recovery of barrier function in ischemiainjured intestine.