Parathyroid hormone (PTH) was recently demonstrated to enhance the HCO3- secretion through the apical anion channel, cystic fibrosis transmembrane conductance regulator (CFTR), but how the HCO3- entered the epithelial cells was not well understood, in part, due to the lack of specific inhibitors of the basolateral HCO3- transporters. Moreover, the function of the PTH-stimulated HCO3- secretion has never been investigated in vivo. Here, we designed three specific pairs of small interfering RNA sequences to simultaneously knockdown three variants of the electrogenic Na+/HCO3- co-transporter (NBCe)-1 in the intestinal epithelium-like Caco-2 monolayer. The results showed that NBCe1 mRNA levels were markedly reduced, and the PTH-induced transepithelial current and voltage changes were diminished after triple knockdown as determined by quantitative real-time PCR and Ussing chamber technique, respectively. An in vivo ligated intestinal loop study further showed that there was an increased fluid secretion, presumably driven by HCO3-transport, in the ileum, but not in jejunum or colon, of rats administered intravenously with 2 mu g/kg body weight of rat PTH 1-34. Therefore, the present results suggested that PTH stimulated intestinal HCO3- secretion, particularly in the ileum, by inducing the basolateral HCO3- uptake via NBCe1. (C) 2011 Elsevier Inc. All rights reserved.