Effects of cold shock and phospholipase A 2 on intact boar spermatozoa and sperm head plasma membranes

Head plasma membranes (HPM) isolated from cryopreserved boar spermatozoa show an excessive fluidization (Buhr et al., Gamete Res 23:441–449, 1989), which might be involved in the loss of fertility. The current study assessed the ability of cold shock (5°C) and phospholipase A 2 (PA 2 ) to duplicate these effects on membrane structure and to affect 45 Ca 2+ uptake and gross morphological characteristics of whole, fresh boar sperm. The HPM from cold‐shocked sperm showed a significantly greater rate of fluidization over time than did HPM from control sperm. Addition of PA 2 (bee or snake venom, 0.1 or 10.0 ng/ml) to HPM from control sperm caused fluidization similar to cold shocking, but to a lesser degree ( P < 0.05). Cold‐shocked intact sperm exhibited severe acrosomal disruption, loss of motility, and increased 45 Ca 2+ uptake relative to control sperm. Addition of PA 2 (bee or snake venom, 0.1, 1.0., 10.0, and 1,000 ng/ml) to control sperm had not effect on gross morphology or motility while maintaining or increasing sperm extrusion of 45 Ca 2+ . Therefore, although PA 2 can, to some extent, duplicate the effects of cold shock on HPM molecular organization, its lipid hydrolytic action is insufficient to cause all the gross disruptions of severe thermal shock. Both PA 2 and cold shock disrupted HPM structure, but only cold shock increased 45 Ca 2+ uptake, suggesting that cold shock may be increasing 45 Ca 2+ uptake in areas other than the head. Cold shock disrupts sperm on three levels; membrane molecular organization, intracellular Ca 2+ regulation, and gross morphology/motility.