Impact of glutaraldehyde versus glutaraldehyde-formaldehyde fixative on cell organization in fish corneal epithelium

Abstract

The purpose of this study was to examine the impact of a low osmolality glutaraldehyde fixative and a high osmolality glutaraldehyde-formaldehyde fixative on the structural organization of a tissue that could be exposed to low and high osmolality environments. The corneas of freshwater trout were prepared for transmission and scanning electron microscopy using either a fixative of 2% glutaraldehyde in 60 mM cacodylate buffer (pH 7.8, 260 mOsm/l) or a fixative prepared by adding 2.5% glutaraldehyde to a solution of 1% formaldehyde and buffering the solution with 0.1 M cacodylate (pH 7.6, 850 mOsm/l; Karnovsky-type fixative). The corneal epithelial cell layer thickness was greater after glutaraldehyde compared to glutaraldehyde-formaldehyde fixation (67 vs 55 μm), as was the thickness of the superficial cells (5.1 vs 3.4 μm) and basal cells (43 vs 38 μm). The intermediate (wing) cells of the epithelium were, however, less thick after glutaraldehyde fixation (15 vs 18 μm). The width of the squamous, intermediate and basal cells was greater following glutaraldehyde fixation with the effect being greatest in the superficial layers and insignificant at the level of the basal cells. The results show that chemical fixatives with extremes of osmolality cannot only produce different cell sizes in a tissue but also determine the overall organization of the cells in a positional-dependent fashion.