Intercellular junctions in thin sections of human senile cataracts

Abstract

The ultrastructural analysis of normal and cataractous lenses is often hindered by incomplete fixation especially of the centers of the lenses. To overcome this limitation, we have achieved good preservation by chemically fixing 50-200 um thick vibratome sections1 of six human senile cataractous lens nuclei obtained after extracapsular surgery. The remaining nuclear core of each lens was deep yellow to amber and contained central opacities. Fresh vibratome sections (15-30 per lens) were examined in the light microscope (FIG. 1) or were prepared for EM. Fixed and embedded whole vibratome sections were usually bisected and examined along a diameter by trimming successive plateaus (FIG. 2 inset) which gave us access to most regions within the lenses.Whole sections in the light microscope (FIG. 1) consistently showed rings of varying density. Undetectable in uncut lenses, the rings may represent slight discontinuities in composition, refractive index or adherence of layers of fiber cells. These rings roughly correspond to the location of cracks in sections which appear after EM processing (FIG.2 & 3). Fiber cells within these lenses generally displayed complex and irregular shapes, but the cells were well preserved with distinct cell boundaries. We emphasize here the common features of the nuclear cataracts which all contained severe enough opacities to warrant surgical removal but in which the cells appeared to remain intact. Adjacent cells interdigitate with irregular protrusions (FIG. 4). Differential cytoplasmic density between neighboring cells is suggestive of variations in refractive index which might cause excessive light scattering. In this same region in FIG. 4 we also note that dense staining material is present in the extracellular space appearing between the undulating membranes of adjacent cells (FIG. 4, inset). We know of no other report of such deposits in normal or abnormal lenses. The thickness of these deposits may also be sufficient to scatter light. A prominent feature of the lens preparations regardless of location is the presence of undulating membranes which are part of tongue-and-groove junctions (FIG. 5). It is noteworthy that the convex side of the curves is consistently well-preserved and is probably the crystalline array of protein noted in other studies, including in human autopsy lenses. It is not known whether cell communication occurs in the nucleus via gap junctions, but structures with the distinctive morphology of gap junctions are present even within senile cataracts (FIG. 5). FIG. 5 also shows a complex clustering of undulating junctions. The multilamellar membrane cluster in FIG.6, which is similar to structures reported in Emory mouse cataracts, is not commonly seen within the mass of lens tissue but is seen at cut surfaces and within cracks where cells are pulled apart.