Effects of glutaraldehyde and critical point drying on the shape and size of erythrocytes in isotonic and hypotonic media.

Scanning electron microscopy (SEM) was applied to studies on osmotically swollen erythrocytes fixed by a method using increasing concentrations of glutaraldehyde (GA), OsO4 as a post fixative, and critical point drying (CPD). This fixation method prevented the osmotic effect of GA itself and preserved the cellular equilibrium shape intact in various media, i.e. discocytes in an isotonic medium and ellipsoids or spheres and ghosts in a hypotonic medium. The discocytes were reduced less in diameter and area than the ellipsoids and spheres during CPD, but the degree of volume shrinkage was of the same magnitude (approx. 73%) regardless of the cell shape. The shrinkage of the discocytes was advanced until the dry volume (approx. 29 microm3) was reached, while the shrinkage of the osmotically swollen cells ceased earlier. A miniaturization process coupled with solvent evaporation is suggested as an explanation for this. The osmotic swelling of erythrocytes was studied quantitatively with the aid of SEM micrographs. The increase in volume was about 60%, which is in agreement with the values obtained by light microscopy for unfixed and GA-fixed cells in the present work and with those reported in the literature.