Rabbit lenses which have been fixed, dehydrated, and dried by a critical-point drying method, can be fractured through the cytoplasm of the differentiating lens fibers, exposing the cell nuclei. The fracture, under these conditions, causes a complete separation of the two membranes of the nuclear envelope from one another, thus exposing entire membrane surfaces (those which line the perinuclear space). These surfaces are not seen in their entirety in typical freeze-fracture or freeze-etch preparations, and consequently have not been described previously. The exposed membrane surfaces which line the perinuclear space have numerous convex structures of approximately 1,000 A, and some larger more irregularly shaped structures. These appear to be fragments of the nuclear pore complexes. Differences in these structures between young fibers and those nearing completion of differentiation is suggested.
Whole rabbit lenses which have been fixed and dried by a critical point drying process were fractured in the dried state, and the exposed internal surfaces were examined with a scanning electron microscope (SEM). Virtually the entire field of fiber endings at a suture can be reproducibly exposed, and examined with the SEM. Other structural features of the lens fiber cells were systematically recorded at various locations from the center of the lens to the equator. The superficial, differentiating fibers tend to fracture through the cytoplasm, exposing the cell nuclei, whereas the mature fibers tend to fracture between adjacent cells, exposing cell surfaces.
The corneal surfaces of marine fish have been previously found to have numerous microprojections, which can best be seen with the scanning electron microscope. Five species of marine teleost were found to have a peculiar form of long curved ridges which are arranged concentrically. Two elasmobranchs, the dogfish and the skate, were found to have microprojections somewhat similar to those seen in the mammalian cornea (Harding, Bagchi, Weinsieder, Peters, 1973, Biol. Bull., 145: 438). In the present study, cell-to-cell variation in the pattern of microprojections has been analyzed in the smooth dogfish (Mustelus canis). Over the surface of an individual cell, the microprojections are typically uniform in appearance and distribution. From cell to cell, however, there may be significant differences in the microprojection pattern. The pattern varies primarily in the length and number of microprojections. Several distinct patterns can be discerned. For example, short numerous microvilli; numerous, relatively long microvilli; sparse, relatively long microvilli, as well as other patterns are found. These different types of cells can have an apparently random distribution. It is suggested that these different patterns reflect stages in the maturation and senescence of the surface epithelial cells.
Energy-dispersive X-ray analysis was used to obtain distribution profiles of Na, K, Cl, P and S in rapidly frozen-dried bulk specimens, and in cryosections of the normal rat lens. Na and Cl are highly concentrated in the capsule, and K and P, in the epithelial cells. Profiles of the entire radius of a lens show relatively high concentrations of K and P in the outermost cells of the lens, with decreasing concentrations through the cortex, and a minimum throughout the nuclear region. S, on the other hand, shows increasing concentrations at deeper locations, with maximum values throughout the nuclear region.
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