Capacitation, the Acrosome Reaction, and Motility in Mammalian Sperm

This chapter reviews capacitation and the acrosome reaction and relates the phenomena with respect to movement patterns of the spermatozoa. Human and hamster sperm may spend time swimming in a pattern that is transitional between activated and hyperactivated. The alterations that occur in the sperm plasma membrane during capacitation include modifications in the structure, organization, and concentration of proteins, phospholipids, and sterols. Comparison of noncapacitated and capacitated spermatozoa by freeze-fracture techniques has revealed a “patching” type of rearrangement of intrinsic proteins in the plasma membrane of the head. Interpretation of results obtained from incubating spermatozoa with putative inducing factors from the cumulus have been fraught with problems, most of which stem from separating the effect of factors on capacitation from their effect on the acrosome reaction. A fraction of preovulatory human follicular fluid has been shown to increase the percentage of true acrosome reactions within seconds of addition to preincubated human spermatozoa.