Does lipid profile explain chilling sensitivity and membrane lipid phase transition of spermatozoa and oocytes?

Ram, fowl and bee spermatozoa, and oocytes of cows and zebrafrsh were used to study lipid membrane profiles, chilling sensitivity and lipid-phase tran sitions. The integrity of the membranes was determined by carboxyfluorescei n diacetate (cFDA) staining following exposure for 15 minutes to low temper atures. Ram and fowl spermatozoa showed differing degrees of loss of membra ne integrity. Surprisingly, bee spermatozoa did not show any sensitivity to chilling, and their membranes remained intact down to 0 degrees C. In bovi ne oocytes (at the GV stage) chilling injury was very severe at 16 degrees C (membrane integrity decreased by 50%). Lipid phase transition (LPT) and membrane fluidity, which were evaluated by Fourier transform infrared (FTLR) microscopy, and fluorescence polarizatio n, showed phase transitions at the same temperatures as caused damage (betw een 30 and 12 degrees C). The membrane lipid profiles showed high concentra tions of polyunsaturated fatty acids (PUFA) in cold-sensitive ram spermatoz oa and zebrafish oocytes, but the ratio between PUFA and saturated fatty ac ids was highest in cold-resistant bee spermatozoa and lowest in cold-sensit ive bovine oocytes. These results suggest a close relationship among cold s usceptibility, lipid phase transition and lipids profile in animal gametes.