Irreversible damage to membrane integrity caused by chilling
during the lipid phase transition is directly related to the quantity
of lipids present [3]. Cholesterol is a major structural lipid constituent
of the membrane and regulates its function. Therefore, the
cholesterol/phospholipid ratio is a vital determinant of plasma
membrane fluidity and stability during cryopreservation [10].
Membranes with high concentrations of cholesterol are more fluid
at low temperatures and consequently more resistant to damage
during cooling [40,41]. To increase membrane fluidity and permeability
at low temperatures, cholesterol can be added to the plasma
membrane, thereby providing an alternative method for increasing
oocyte tolerance for cryopreservation