Arav, A., Institute of Animal Science, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel
Pearl, M., Institute of Animal Science, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel
Zeron, Y., Institute of Animal Science, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel

Ram, fowl and bee spermatozoa, and oocytes of cows and zebrafish were used to study lipid membrane profiles, chilling sensitivity and lipid-phase transitions. The integrity of the membranes was determined by carboxyfluorescein diacetate (cFDA) staining following exposure for 15 minutes to low-temperatures. Ram and fowl spermatozoa showed differing degrees of loss of membrane integrity. Surprisingly, bee spermatozoa did not show any sensitivity to chilling, and their membranes remained intact down to 0°C. In bovine oocytes (at the GV stage) chilling injury was very severe at 16°C (membrane integrity decreased by 50%). Lipid phase transition (LPT) and membrane fluidity, which were evaluated by Fourier transform infrared (FTIR) microscopy, and fluorescence polarization, showed phase transitions at the same temperatures as caused damage (between 30 and 12°C). The membrane lipid profiles showed high concentrations of polyunsaturated fatty acids (PUFA) in cold-sensitive ram spermatozoa and zebrafish oocytes, but the ratio between PUFA and saturated fatty acids was highest in cold-resistant bee spermatozoa and lowest in cold-sensitive bovine oocytes. These results suggest a close relationship among cold susceptibility, lipid phase transition and lipids profile in animal gametes.