This may explain why heparin interferes with bovine sperm-oviduct binding. An issue for further research is to decipher whether the sperm release is caused i) directly by extracellular GAG or ii) indirectly via sperm capacitation that induces sperm surface changes and subsequently causes the release, or iii) a combination of both processes.
Bicarbonate-enriched Tyrode media induced capacitation of approximately 40% of the bovine sperm cells, as also did heparin during the 4-h incubation, as observed by CTC staining (this study). This indicates that bicarbonate primarily is responsible for the capacitation changes demonstrated by the CTC staining (see also). High levels of glucose only partly inhibited the capacitation response (this study) but did not block capacitation as reported earlier. It is likely that this discrepancy is caused by the method of detecting capacitation: Medeiros and Parrish used a panel of lectins to detect heparin-induced surface changes in lectin-binding topology and intensity. Probably, such changes in lectin interactions are in part a sequential response occurring later than the CTC response.