The osmotic effect of glutaraldehyde during fixation. A transmission electron microscopy, scanning electron microscopy and cytochemical study

Abstract

In order to interpret properly the ultrastructure of cells as revealed by various electron microscopic methods, it is of fundamental importance that fixation be accompanied by a minimal distortion of cell structures. Furthermore, any artifacts which are inadvertently produced should be recognized for what they are. For the study of mammalian cells and tissues, fixation in buffered glutaraldehyde followed by postfixation in osmium tetroxide is now a widely accepted method. During the primary fixation in glutaraldehyde, the osmotic conditions will greatly affect the fixation result (6, 7, 12, 18, 19, 24-26). Postfixation in osmium tetroxide results in the total destruction of the cell membrane semipermeable properties and thus the effect of the tonicity of the fluid surrounding the cells following this t reatment can be expected to be negligible (6, 15, 29). Although a number of papers have been devoted to studies of the relationship between the cellular ultrastructure and the osmotic pressure of the glutaraldehydebased fixatives [for reviews see (16, 27)] there is no general agreement as to the contribution of the aldehyde to the effective osmotic pressure of the fixative (13). By effective osmotic pressure is meant the osmotic pressure caused by those mole-