Aim:  We compared the distribution and putative association of Cl^– channel transport, CFTR mRNA transcripts, and Na⁺ channel (ENaC)α‐ and β‐subunit mRNA transcripts in villus and crypt epithelial cells of duodenum, with corresponding surface and crypt cells of colon from sodium‐depleted rats.

Methods:  Cells were loaded with ³⁶Cl^– and forskolin‐stimulated efflux was determined. RT‐PCR was performed for CFTR mRNA transcripts and ENaC α‐ and β‐subunit mRNA. Duodenal epithelial cell response to VIP was assessed by measuring intracellular cAMP.

Results:  Forskolin‐stimulated Cl⁻ efflux occurred with decreasing magnitude in duodenal crypt, duodenal villus, colonic crypt and colonic surface cells in Na⁺‐depleted animals. CFTR expression was correlated directly with Cl⁻ efflux (r = 0.91, P < 0.01). Na⁺ channel α‐subunit was expressed in colon and duodenum in animals fed diets with a high or low sodium content. While the β‐subunit mRNA was detected in the colon of sodium‐restricted rats, it was absent in the duodenum under control conditions and after Na⁺ restriction. There was an inverse correlation between mRNA transcripts for CFTR and the ENaC α‐subunit (r = −0.93, P < 0.003) and β‐subunit (r = −0.91, P < 0.004) in colon. VIP‐stimulated cAMP in duodenal epithelial cells was greater in crypt than villus (P < 0.05).

Conclusion:  Cl⁻ efflux, CFTR transcription and forskolin‐stimulated cAMP activity occur in both crypt and villus epithelial cells in duodenum. Possible interaction between CFTR and Na⁺ channels is apparently limited to parts of the colonic crypt. Lack of duodenal β‐subunit expression makes ENaC activity unlikely.