A MORPHOLOGICAL AND FUNCTIONAL-STUDY OF FUSIBILITY IN ROUND-HEADED SPERMATOZOA IN THE HUMAN

Objective: To study the molecular origin and functionality of the plasma membrane of round-head spermatozoa in the human. Design: Clinical and laboratory study. Setting: Patients in a clinical and academic environment. Patients: Men with round-head spermatozoa. Results: Pisum sativum lectin homogeneously stains the surface of round sperm; however, the staining pattern and transmission electron microscopy show that the plasma membrane does not alter after exposure to the calcium ionophore A23187. In a clinical program, round-head spermatozoa injected subzonally into metaphase II oocytes with or without pretreatment with the fusogen polyethylene glycol did not bind or fuse to the oocyte surface. Conclusion: The data suggests that plasma membrane fusion in human gametes is regulated by specific surface molecules and that exposure of these molecules on the sperm surface cannot be triggered by elevating intracellular calcium alone.