Calcium ionophore A23187 as a probe for freeze-fracture studies of membrane changes in the head of human spermatozoa.

The membranes of the head of human spermatozoa were examined after incubating the sperm with and without inophore A23187 and calcium ions, using freeze-fracture electron microscopy. After exposure to ionophore and calcium there was a remarkable rearrangement of the intramembraneous particles, especially in the plasma membrane. Buckling of the plasma membrane occurred prior to breaking away from the outer region of the sperm head. The outer acrosomal membrane bubbled and broke down to form vesicles, and blebbing of the inner acrosome membrane also occurred. The nuclear envelope degenerated and often displayed an undulating topography.