[Regional differences in the ciliary body of cattle. An electron microscopy and histochemical study].

The bovine ciliary body was investigated by scanning and transmission electron microscopy. The number of cell organelles (mitochondria, rough endoplasmatic reticulum and Golgi complexes) of the nonpigmented (UPE) and the pigmented (PE) epithelium were quantitatively evaluated. Histochemically the activity of carbonic anhydrase (CA) and Na+/K(+)-ATPase was localized within the UPE and PE. As a result of this study, the bovine ciliary body was found to be organized similar to the human and primate ciliary body and can be divided into 4 zones: (1) transition zone between the iris and ciliary body; (2) prelenticular portion of the pars plicata; (3) postlenticular portion of the pars plicata; (4) pars plana. In zone 2 the UPE and PE are filled by numerous mitochondria and show extensive infoldings of the basal cell membranes, which react positively for CA and Na+/K(+)-ATPase, indicating that these cells are involved in the secretion of aequous humor. The transition zone is covered by extremely flat UPE cells and might influence the composition of the aqueous humor by reabsorption rather than secretion. In the postlenticular pars plicata, the number of mitochondria, membrane infoldings and enzyme activity decreases, while the number of rER and Golgi complexes, which are necessary for the synthesis of proteins and proteoglycans, increases. In the pars plana, the UPE is filled completely with filaments pointing to the mechanical strain caused by insertion of the zonular fibers.