Immunohistochemical localization of carbonic anhydrase isozyme II in the gustatory epithelium of the adult rat

The distribution of carbonic anhydrase isozyme II (CA II)-like immunoreacti vity (-LI) in the gustatory epithelium was era mined in the adult rat. In t he circumvallate and foliate papillae, CA II-LI was observed in the cytopla sm of the spindle-shaped taste bud cells, with weak immunoreaction in the s urface of the gustatory epithelium. No neuronal elements displayed CA II-LI in these papillae. There was no apparent difference in the distribution pa ttern between the anterior and posterior portions of the foliate papillae. In immunoelectron microscopy, immunoreaction products for CA II were diffus ely distributed in the entire cytoplasm of the taste bud cells having dense round granules at the periphery of the cells. No taste bud cells displayin g CA II-LI were detected in the fungiform papillae, but a few thick nerve f ibers displayed CA II-LI. In the taste buds of the palatal epithelium, neit her taste bud cells nor neuronal elements exhibited CA II-LI. The present r esults indicate that CA II was localized in the type I cells designated as supporting cells in the taste buds located in the posterior lingual papilla e of the adult animal.