NHE-1 isoform of the Na+/H+ antiport is expressed in the rat and rabbit esophagus.

Abstract

Rabbit esophageal cells show an amiloride-sensitive Na+/H+ antiporter activity. Several distinct molecular isoforms of the Na+/H+ exchanger family (NHE) are reported to be present in the gastrointestinal tract of rats and rabbits. The aim of this study was to examine which isoforms are present in rabbit and rat esophageal cells and whether this isoform could be up-regulated by serum factors. Specific primers designed from the rat NHE-1-4 and the rabbit NHE-1-3 isoform sequences were used for reverse-transcription polymerase chain reaction analysis with RNA from rabbit and rat esophageal cells. Ribonuclease protection assay was used to determine the serum-induced up-regulation of NHE-1. Antibodies raised against the NHE-1 C-terminal fragment were used for Western blotting with rabbit esophageal membranes. In both the rat and rabbit esophagus, only the NHE-1 isoform messenger RNA could be detected. The NHE-1 messenger RNA, detected in rabbit esophageal cells grown from tissue explants, was up-regulated by serum factors. The antibody detected a 95-kilodalton protein in esophageal cell membranes. The rabbit and rat esophagus exclusively express the NHE-1 isoform, hypothesized to be involved in cytoplasmic pH regulation. Therefore, the results of this study suggest a role for NHE-1 in protecting cells against gastric acid that is refluxed into the esophagus.