The distribution of carbonic anhydrase II in human, pig and rat oesophageal epithelium.

Carbonic anhydrase II (CA II) is present in human oesophageal epithelial cells and probably involved in protecting the mucosa against acidic gastric refluxate. If this is the case, then it is likely that the enzyme will be more concentrated at or near the gastro-oesophageal junction. To answer this question, and determine whether CA II is present and similarly distributed in other species, we also examined the oesophageal epithelium of the rat and pig. In the rat, CA II was largely absent from the oesophageal epithelium, but present in the stratified squamous epithelium of the gastric forestomach as an approximately 2 mm-long collar around the entrance to the corpus, a site that roughly corresponds to the gastro-oesophageal junction in other animals. The enzyme was present mainly in basal and prickle cells. In upper and middle pig oesophagus, CA II was largely confined to basal cells and isolated groups of stratified superficial prickle cells. CA II-containing epithelial cells were highly concentrated in the thickened epithelium at the gastro-oesophageal junction (about four-times thicker than upper or middle). Reactive cells were present throughout the depth of the epithelium, but noticeably more concentrated in the basal and superficial prickle cell layers. CA II was also prominent in the most superficial cell layers in islands of the oesophageal mucosa within the gastric cardia. In man, CA II was confined largely to the basal half of the epithelium in the upper and middle regions of oesophagus. The distribution of CA II at the gastro-oesophageal junction took different forms. In general, there were more CA II-reactive cells at or closer to the lumen. The superficial prickle cell layers tended to exhibit more CA II than the deeper layers, with basal and epibasal cells containing little or no enzyme. In other regions of the same specimens, CA II-containing cells were present from the basal to the most luminal layers. If CA II in oesophageal epithelial cells in the region of the gastro-oesophageal junction (or in the case of the rat the forestomach/corpus junction) is important in the defence against refluxate, then it is in a vulnerable site, since bile salts are potent inhibitors of the enzyme. The action of bile salts on CA II may be an important factor in the initiation of oesophageal disease.