The mature spermatozoon is not considered to have any significant capacity for de novo expression of internally localized membrane components. Thus the increased capacity for binding sZP and the extension of the surface area over which binding occurred would seem to be due to exposure, activation, or increased affinity of already existing structures in the sperm membrane. These alterations could result respectively from unmasking, from oligomerization, or from changes of the physical microenvironment during dynamic reorganization of the plasma membrane architecture. buy flovent inhaler
Ashworth et al. have described alterations in specific lectin-binding sites on boar sperm that develop during incubation under conditions of incubation essentially similar to those used in the present study; the lectin-binding changes seemed to be related to loss of seminal plasma-derived coating proteins and to concomitant unmasking of underlying components. However, IVF conditions also induce dynamic reorganization of the plasma membrane lipid bilayer , and changes in the lipid architecture could affect the ability of membrane components to migrate to new locations within the bilayer, with resultant altered binding characteristics. Gadella and colleagues have demonstrated a migration of glycolipids within the boar sperm plasma membrane, from the apical ridge towards the equatorial subdomain, which parallels closely our own observations of the extension of the surface on which sZP binding occurred. The glycolipid migration was also dependent on Ca2+ and took place during incubation under IVF conditions with a time course similar to the sZP binding change we have described.