Boar spermatozoa within the oviductal environment (II): Sperm capacitation

Abstract

Around ovulation, a set of changes leads to a destabilisation of the sperm membrane that results in the release of spermatozoa from the oviductal reservoir (see Chap. 6). This destabilisation of the sperm membrane is an early step of the capacitation process, is mediated by bicarbonate, and allows AQN-1 to be shed from the surface. After being released from sperm reservoir, spermatozoa freely swim from the isthmus towards the ampulla/ampullary-isthmic junction where, amongst others, the following crucial and sequential events take place: (1) completion of sperm capacitation, (2) binding of spermatozoa to the ZP of the oocyte, (3) acrosome exocytosis and (4) further membrane fusion. The present chapter deals with the first issue, and thus focuses on the changes that the spermatozoon undergoes during capacitation. These changes, which can be separated between early/fast and late/slow, entail the activation of several signalling pathways, the increase of certain intracellular messengers, such as Ca2+ and cAMP, the reorganisation of proteins and lipids of sperm plasmalemma, and changes in motility patterns. Finally, destabilisation of the acrosomal sperm head membrane increases the sperm's ability to bind the zona pellucida of the oocyte.