In the cornea, biotC incorporation was detected in the epithelium,
predominantly within the intercellular spaces but also in the cytoplasm
of the epithelial cells and along their basement membranes. Keratocytes
in the superficial layers of the corneal stroma were also labeled (
Fig. 1A ). TGase activity was visualized in the conjunctival epithelium,
especially within intercellular spaces
(Fig. 1B) . Further cross-linking
of biotC was detected in the walls of stromal vessels. In the sclera
the presence of TGase activity was restricted to the endothelial lining
of intra- and episcleral blood vessels
(Fig. 1C) and single scattered
cells, presumably fibroblasts, between the collagen lamellae. In the
trabecular meshwork TGase activity was found in association with the
trabecular endothelial cells, particularly in the posterior part of the
meshwork (
Fig. 2A ) and in association with the endothelial cells lining Schlemm’s
canal, collector channels, and intrascleral aqueous veins. In the iris
BiotC incorporation was prominent in the smooth muscle cells of the
dilator and sphincter muscles, in the vascular endothelial cells of
stromal vessels, and along delicate fibrillar structures in the stroma,
which were particularly concentrated in the anterior boarder layer
(Fig. 1D) . Extensive cross-linking was apparent along most ciliary body
structures, especially along the zonular fibers covering the surface of
the ciliary epithelium, and also in the ciliary muscle cells and the
outer limiting membrane (i.e., the basement membrane of the pigmented
ciliary epithelium;
Figs. 2A 2B 2C 2D ). The inner limiting membrane
(the basement membrane of the nonpigmented epithelial layer) expressed
some TGase activity in the pars plana region only. The nonpigmented
epithelial layer was essentially negative in the pars plana area. The
stromal connective tissue of the ciliary body was characterized by
TGase activity in stromal cells (presumably fibrocytes), in vascular
endothelial cells, and along extracellular fibrillar strands. In the
lens biotC incorporation was strong in the zonula lamella on the
surfaces of the lens capsule and in the zonular fibers adhering to it
and to a minor extent in the lens epithelial cells. Some TGase activity
was also detected in the equatorial portions of the lens capsule (not
shown). The choroid expressed high-level TGase activity within cells
and fibrous strands of the connective tissue, within Bruch’s membrane,
and within vascular endothelial cells of the choriocapillaris (
Fig. 3A ). TGase activity in the retina was strictly confined to the
endothelial lining of retinal capillaries
(Fig. 3A) . Activity in the
optic nerve was localized to capillaries within the glial columns of
the prelaminar portion, to the cribriform plates of connective tissue
in the laminar portion, and to the connective tissue septa including
their vasculature in the postlaminar portion
(Fig. 3C) . Additional
cross-linking was found in the optic nerve meninges, particularly the
pia mater and arachnoidea (not shown). EDTA completely inhibited biotC
incorporation, demonstrating the specificity of the reaction (
Figs. 2B ,
3B , and
3D ).