NHE-1 ISOFORM OF THE NA+ H+ ANTIPORT IS EXPRESSED IN THE RAT AND RABBIT ESOPHAGUS/

Background & Aims: Rabbit esophageal cells show an amiloride-sensitive Na+/H+ antiporter activity. Several distinct molecular isoforms of th e Na+/H+ exchanger family (NHE) are reported to be present in the gast rointestinal tract of rats and rabbits. The aim of this study was to e xamine which isoforms are present in rabbit and rat esophageal cells a nd whether this isoform could be upregulated by serum factors. Methods : Specific primers designed from the rat NHE-1-4 and the rabbit NHE-1- 3 isoform sequences were used for reverse-transcription polymerase cha in reaction analysis with RNA from rabbit and rat esophageal cells. Ri bonuclease protection assay was used to determine the serum-induced up regulation of NHE-1, Antibodies raised against the NHE-1 C-terminal fr agment were used for Western blotting with rabbit esophageal membranes . Results: In both the rat and rabbit esophagus, only the NHE-1 isofor m messenger RNA could be detected. The NHE-1 messenger RNA, detected i n rabbit esophageal cells grown from tissue explants, was up regulated by serum factors. The antibody detected a 95-kilodalton protein in es ophageal cell membranes. Conclusions: The rabbit and rat esophagus exc lusively express the NHE-1 isoform, hypothesized to be involved in cyt oplasmic pH regulation. Therefore, the results of this study suggest a role for NHE-1 in protecting cells against gastric acid that is reflu xed into the esophagus.