Dynamics of Carbohydrate Affinities at the Cell Surface of Capacitating Bovine Sperm Cells

In vivo capacitation of eutherian sperm cells coincides with changes in carbohydrate-dependent interaction with the oviduct epithelia (fucose-dependent for bovine). Heparin-like glycosaminoglycans (GAG) secreted by the oviduct compete for sperm-oviduct binding and are believed to release capacitated sperm cells from oviduct epithelia. A biochemical assay to quantify the specificity and dynamics of carbohydrate-mediated bovine sperm-oviduct binding is developed. Sperm apical plasma membranes (SPM) were purified by a factor eight and biotinylated carbohydrate probes were used for quantitative evaluation of carbohydrate binding. SPM of fresh sperm showed >12 times higher binding capacity for biotinylated fucose than for LewisA. SPM from fresh sperm also efficiently bound biotinylated fucoidan and mannan. Binding of biotinylated fucose could be inhibited by various mono- and oligosaccharides such as fucoidan, mannan, heparin, maltose, and, to a lesser extent, glucose (50% binding at 0.2 mM, 2 mM, 0.3 (mu)g/ml, 15 mM, 50 mM, respectively). SPM from sperm cells that were in vitro capacitated for 4 h in bicarbonate-enriched media (either with or without 10 (mu)g/ml heparin) showed a 70–85% reduction in fucose binding. This was also achieved by follicular fluid or by GAG, both obtained from dominant follicles. Total follicular fluid was much more potent in competing with fucose for sperm binding than the isolated GAG moieties (50% competition at 0.02 (mu)g/ml, 20 (mu)g/ml based on number of GAG moieties, respectively). These results support the hypothesis that in vivo capacitation of sperm cells is regulated by carbohydrate moieties similar to those regulating sperm-oviduct adhesion.