Cold Shock
When sperm cells are cooled too fast to 5°C, they undergo irreversible damage called cold shock. The damage to the sperm cells is caused by changes in the plasma membrane as it is cooled. The lipid bilayer membrane goes from a liquid-crystalline (fluid) state to the gel state (restricted movement of proteins and lipids).
Cold shock causes abnormal motility patterns, loss of motility and acrosomal damage. In the diagram below you can see the changes in the lipid bilayer as the cell is cooled to fast to 5°C and rewarmed to 37°C. When the membrane is rapidly cooled there is a clustering of the lipids which favor nonbilayer formation. When the sperm are warmed these lipid form areas of nonbilayer (Hex phase) in the membrane which disrupts the normal function of the membrane. The proteins were also originally surrounded by specific phospholipids. Upon rewarming, the proteins become surrounded by different lipids and the protein function is disrupted. These problems then lead to the changes in motility, acrosome damage and eventual sperm death before fertilization can occur. In slow cooling the membrane returns to its original structure upon rewarming.
Effect of Cooling Sperm to Rapidly
