Capacitation


 * This article is about a biological process related to reproduction; for the other use, see Capacitation (NGO).

Capacitation is the final step in the maturation of mammalian spermatozoa and is required to render them competent to fertilize an oocyte. This step is a biochemical event; the sperm move normally and look mature prior to capacitation. In vivo this final step typically occurs after ejaculation, in the female reproductive tract. In vitro, capacitation can occur in sperm that have either undergone ejaculation or have been extracted from the epididymis. Non-mammalian spermatozoa do not require this capacitation step and are ready to fertilize an oocyte immediately after release from the male.

The discovery of this process was independently reported in 1951 by both Min Chueh Chang and C.A. Austin.

Historically, the term "capacitation" has evolved in meaning and this should be taken into account when consulting sources.

Capacitation involves the destabilisation of the sperm head membrane by the removal of sterols (cholesterol) and non-covalently bound epididymal/seminal glycoproteins. The result is a more fluid membrane with an increased permiability to Ca2+. An influx of Ca2+ produces increased intracellular cAMP levels and thus, an increase in motility. Hyperactivation is also part of capacitation and is the result of the increased Ca2+ levels.

By secreting sterol binding albumin, lipoproteins, proteolytic and glycosidasic enzymes, the uterus aids in the steps of capacitation.