DO TREHALOSE AND DIMETHYL-SULFOXIDE AFFECT INTERMEMBRANE FORCES

The sugar trehalose is produced in some organisms that survive dehydra tion and desiccation, and it preserves the integrity of membranes in m odel systems exposed to dehydration and freezing. Dimethyl sulfoxide, a solute which permeates membranes, is added to cell suspensions in ma ny protocols for cryopreservation. Using a surface forces apparatus, w e measured the very large, short-range repulsion between phosphatidylc holine bilayers in water and in solutions of trehalose, sorbitol, and dimethyl-sulfoxide. To the resolution of the technique, the force-dist ance curves between bilayers are unchanged by the addition of trehalos e or sorbitol in concentrations exceeding 1 kmol.m(-3). A relatively s mall increase in adhesion in the presence of trehalose and sorbitol so lutions may be explained by their osmotic effects. The partitioning of trehalose between aqueous solutions and lamellar phases of dioleylpho sphatidylcholine was measured gravimetrically. The amount of trehalose that preferentially adsorbs near membrane surfaces is at most small. The presence of dimethyl sulfoxide in water (1:2 by volume) makes very little difference to the short-range interaction between deposited bi layers, but it sometimes perturbs them in ways that vary among experim ents: free bilayers and/or fusion of the deposited bilayers were each observed in about one-third of the experiments. (C) 1994 Academic Pres s, Inc.