Ultrastructural localization of carbonic anhydrase in the chorioallantoic membrane by immunocytochemistry

Carbonic anhydrase was localized in the chick embryo chorionic ectoderm at the ultrastructural level by immuno-cytochemistry. Preembedding staining of whole tissue was performed. The enzyme was present in the cytoplasm, on the membranes of apical vesicles, and on the membranes of microvilli in villus cavity cells, cells that may be involved in acid secretion and subsequent dissolution of the egg shell. In sinus covering cells, the enzyme is solely in the cytoplasm. The location of the enzyme in the thin cytoplasmic arms of the sinus covering cells is consistent with the role in nonrespiratory CO2 release.