Immunohistochemical localization of carbonic anhydrase isozymes in the rat carotid body.

The rat carotid body was immunohistochemically stained for carbonic anhydrase I, II and III (CA-I, CA-II and CA-III). Immunoreactivity for CA-I was distributed in type I cells, type II cells and nerve bundles. Smooth muscle cells and endothelial cells of blood vessels were also strongly stained for CA-I. CA-II immunoreactivity was distinctly positive in type I cells and nerve bundles. Vascular smooth muscle cells were weakly positive, and type II cells were negative for CA-II. CA-III immunoreactivity was identified in type I cells and vascular smooth muscle cells. Our results suggest that carbonic anhydrase isozymes in type I cells play an important role in chemoreception for hypercapnia. Immunoreactivities for CA-I and CA-II in the nerve fibres may participate in the synergic action of carotid sinus nerve between hypoxic and hypercapnic stimuli.