The effect of chilling on membrane lipid phase transition in human oocytes and zygotes.
BACKGROUND
Chilling injury occurs when the cell membrane undergoes a transition from the liquid state to the gel state. Human oocytes and single-cell zygotes are of similar shape and size but the post-thawing survival rate of oocytes is poorer. We set out to investigate the possible difference in membrane lipid phase transition (LPT) temperature between the two cell types.


METHODS
The LPT temperature was measured with a Fourier Transform Infrared analyser, which detects the change in the vibration frequency of the CH2 bond stretches of the membrane lipid molecules during temperature change. The LPT temperatures of unfertilized human oocytes, in vitro-matured oocytes, and immature germinal vesicle (GV) stage oocytes were compared with that of abnormally fertilized human zygotes.


RESULTS
The LPT temperatures of zygotes and of mature and immature GV oocytes differ significantly from each other (10.0 +/- 1.2, 16.9 +/- 0.9 and 24.4 +/- 1.6 degrees C respectively; P < 0.05).


CONCLUSIONS
Zygotes show a higher resistance to chilling injury compared to oocytes at different developmental stages; this might explain the relatively poor survival rates of cryopreserved human oocytes and indicates the necessity to adjust the cryopreservation protocols in order to minimize cryoinjury.
Ghetler
Yehudith
Y
Department of Cell and Developmental Biology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
Yavin
Saar
S
Shalgi
Ruth
R
Arav
Amir
A
D002462:Cell Membrane / Q000378:metabolism*; D015925:Cryopreservation / Q000379:methods*; D046149:Embryo Culture Techniques; D005306:Fertilization; D005307:Fertilization in Vitro; D006801:Humans; D008055:Lipids / Q000737:chemistry; D009865:Oocytes / Q000166:cytology / Q000378:metabolism*; D010743:Phospholipids / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D020554:Sperm Injections, Intracytoplasmic; D013696:Temperature; D013997:Time Factors; D015053:Zygote / Q000378:metabolism*
D008055:Lipids; D010743:Phospholipids