Induction of Acrosomal Reaction in Sperm with lonophore A23187 and Calcium

The acrosome reaction was induced in ram, rabbit, and human sperm by incubating with the ionophore A23187 plus calcium ions, although the percentage of reacted sperm was different for each species: 90% in ram, 38% in rabbit, and 69% in man. Fusion of the outer acrosomal and plasma membranes of ram and rabbit sperm formed vesicles, but in human sperm only the outer acrosomal membrane was involved in vesiculation. Acrosin was lost from ram, rabbit, and human sperm after treatment with ionophore plus calcium. Ionophore alone induced the reaction in only 35% of ram sperm, 20% of human sperm, and 12% of rabbit sperm. On exposure to A23187 alone, the acrosome of unreacted rabbit sperm bulged and the acrosome and nuclear membrane of human sperm were often lifted away from the nucleus. The percentage of mammalian sperm undergoing the acrosome reaction in the presence of calcium alone, was very low.