Although heparin had no effect on the binding of the uncapacitated sperm to the oviductal epithelium, it was recently shown that heparin acts as a strong inhibitor of sperm binding and also a quick releaser of sperm bound to the oviduct epithelium (this study, ). Heparin (and fucoidan) induce an increase in flagellar-beat frequency and also high linear motility during sperm release from the bovine oviduct. We demonstrated that heparin is a very strong inhibitor of fucose-PAA-biotin binding to SPM even at concentrations as low as 0.01 |xg/ml (1000 times lower than the standard heparin concentration at capacitation conditions). This inhibitory effect is most likely due to competitive binding of heparin to the fucose-binding ligand present in the SPM.
In this respect, indeed, the binding competition between fucose and heparin was independent from sperm capacitation. Therefore, our experiments support the observation that heparin interferes in binding of the uncapacitated SPM to the specific carbohydrate moieties of the oviductal epithelial cells. Interestingly, a bull sperm protein, PDC-109, has been described as being involved in sperm binding to the oviduct and to have affinity for both fucose as well as heparin.