Osmotic properties of the rabbit corneal endothelium and their relevance to cryopreservation

The process of cryopreservation subjects cells to gross changes in the composition of the solution that surrounds them, changes that cause the cells first to shrink and then to swell by an osmotic mechanism. Empirical methods have been developed that permit many cells to survive freezing and thawing, but the cornea, which is crucially dependent upon the function of its endothelial monolayer, has proved quite refractory. In this paper we explore the osmotic response of the corneal endothelium of the rabbit to solutions ranging in osmolality from 0.25 to 8.6 × isotonic. Boyle van't Hoff behavior was observed between 0.43 and 8.6 × isotonic, and there was an apparent nonosmotic volume of 33.6%. However, ultrastructural damage was observed at the limits of this range, and it appeared that the tolerated range was 0.64–4.4 × isotonic. We show the extent to which dimethyl sulfoxide (Me₂SO) would be expected to moderate changes in volume during freezing and suggest that its initial concentration should be at least 2M to prevent excessive shrinkage. We also show that cell swelling during removal of Me₂SO is especially likely to be hazardous.