STABILITY OF THE LIPID COMPONENT OF TROUT SPERM PLASMA-MEMBRANE DURING FREEZE-THAWING

Trout spermatozoa are very sensitive to freeze-thawing, and the best c ryoprotectants tested until now have a highly variable protective effe ct. It is not rare that only 10% of the frozen spermatozoa display an undamaged plasma membrane. The aim of this study was to determine whet her membrane fragility of rainbow trout sperm (Oncorhynchus mykiss) is due to membrane lipid phase transitions, as postulated for other spec ies, and to explore stabilization of membrane phospholipids by the com ponents present in the freezing extender. Using Fourier transform infr ared spectroscopy, we showed that the plasma membrane exhibited a stea dy decrease in fluidity as temperature decreased. A clear phase transi tion was observed only with purified membrane phospholipids. Stability of frozen-thawed liposomes made with trout plasma membrane phospholip ids was assessed. Although dimethyl sulfoxide stabilized the liposomes better than glycerol, it showed negative interactions with other comp onents added to the extender such as TES (N-tris[hydroxymethyl]methyl- 2-aminoethanesulfonic acid) or phosphate. We propose that membrane pho spholipid liposomes provide an interesting way to assess the compatibi lity between various molecules when testing a freezing extender. (C) 1 997 Academic Press.