Lipid dynamics in the plasma membrane of ram and bull spermatozoa after washing and exposure to macromolecules BSA and PVP

Seminal plasma proteins and macromolecules in the external medium have a major influence on the functionality of sperm plasma membranes. In this investigation we have examined their effects on lipid diffusion in the surface membrane of ram and bull spermatozoa as measured by fluorescence recovery after photobleaching (FRAP). Results show that progressive removal of seminal plasma from ram spermatozoa by repeated centrifugation and resuspension in media ± 4% bovine serum albumin (BSA) or 0.4% polyvinlypyrrolidone (PVP) causes a reduction in lipid diffusion in all regions of the membrane. By contrast, bull sperm membranes respond with an increase in diffusion in all regions. Repeated washing of bull spermatozoa whose membranes were previously immobile (i.e., showed no recovery after FRAP) restored lipid diffusion suggesting an inhibitory effect of seminal plasma proteins. Further analysis by atomic force microscopy revealed a close association between BSA and the plasma membrane. It is concluded that diffusion of lipids in the plasma membrane of ejaculated ram and bull spermatozoa is influenced by seminal plasma proteins and the composition of the suspending medium. Mol. Reprod. Dev. 59:306–313, 2001. © 2001 Wiley-Liss, Inc.