INTER-CELLULAR JUNCTIONS IN CILIARY EPITHELIUM

  • 1 January 1978
    • journal article
    • research article
    • Vol. 17  (10) , 958-981
Abstract
The fine structure of the intercellular junctions in the ciliary epithelium of rhesus monkeys [Macaca mulatta] and rabbits was studied with conventional EM of thin-sectioned specimens and the freeze-fracturing technique. In the rhesus monkey, a zonula occludens, zonula adherens, gap junctions and desmosomes interconnect the nonpigmented cells, whereas gap junctions, puncta adherentia and desmosomes connect pigmented to nonpigmented cells, and pigmented cells to one another. In the rabbit, desmosomes connect pigmented to nonpigmented cells, and pigmented cells to one another. In the rabbit, desmosomes are absent between nonpigmented cells, and substituted for by puncta adherentia. The zonula occludens between nonpigmented cells greatly varies in its complexity in different regions of the cell perimeter, and in places, it may consist of very few intramembrane strands; this suggests that the ciliary epithelium is relatively leaky to ions and small molecules. Gap junctions are ubiquitous in the ciliary epithelium and particularly numerous at the interface between pigmented and nonpigmented layers; this finding indicates that the cells of the cilary epithelium are joined in a metabolic syncytium. All gap junctions are characterized by the crystalline configuration which is typical of the uncoupled state; furthermore, in specimens fixed by immersion, they may be curved or deeply invaginated. Since curved and invaginating gap junctions are rare after perfusion fixation, this distortion of the cell surface may be caused by uncoupling and take place in the time interval elapsing between interruption of the blood supply and arrival of the fixative fluid. Puncta adherentia resemble zonulae adherentes in their structural details but are macular in shape instead of encompassing the cell perimeter in a beltlike fashion. In contrast with desmosomes, the intercellular cleft of puncta adherentia has an irregular width and contains opaque material, but this never gives rise to the central band typical of desmosomes. On the inner aspect of the junctional membranes, there is a layer of fluffy material but no plaque of insertion for a bundle of tonofilaments. Puncta adherentia have no representation in the interior of the plasmalemma and are intimately associated with cytoplasmic microfilaments. They probably anchor to the plasmalemma the contractile apparatus of the cilary epithelial cells.

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