Previous studies have used cell culture models, intrarectal instillation of toxins in mice, ileal loop injections in rabbits, and human patient samples to examine the effects of toxins and CDI on tight junctions and the expression of key ion transporters.11,13,15,16,19,20 These studies implicate increased paracellular leakage, Cl– secretion, and/or expression loss of electroneutral ion exchangers NHE3 and DRA as potential causes of diarrhea. The gene discussed is SLC9A3; the disease is clostridium difficile infection.