Specific localisation of gap junction protein connexin 32 in the gastric mucosa of horses

In the glandular stomach, gap junctional intercellular communication (GJIC) plays an important role in the gastric mucosal defense system, and loss of GJIC is associated with ulcer formation. In spite of the high incidence of gastric ulcers in horses, particularly at pars nonglandularis, the presence of gap junctions in the equine stomach has not yet been studied. The objective was to obtain basic data on the distribution of gap junction protein connexin 32 (Cx32) in the different regions of normal equine gastric mucosa. Samples of mucosa were taken from seven horses at cardiac, fundic, and pyloric region and pars nonglandularis. To detect Cx32, immunohistochemical staining and Western blot analysis were performed. Corresponding mRNA was shown by RT-PCR and localised in tissue sections by in situ hybridisation. Cx32 was found in the glandular regions, whereas it was not detectable in squamous mucosa. Within the glandular epithelium, Cx32 was abundant in surface and foveolar cells and decreased towards the proliferative zone of the glands. These results suggest that gap junctions develop during the maturation of surface cells. Whether the lack of Cx32 at pars nonglandularis contributes to its susceptibility for developing ulcers, has to be further elucidated.