FIGURE 3.

Schematic representation of the biochemical and electrophysiological changes during sperm capacitation in the female genital tract. Capacitation confers the sperm cells a hyperactivated motility characterized by an increased flagellar amplitude and beating frequency, and the ability to perform the acrosomal reaction and to specifically recognize and interact with oocyte. This functional activation is mainly induced by HCO₃^–, Ca²⁺ and Cl^– influxes, which trigger biochemical and electrophysiological changes in the cytoplasm and the whole plasma membrane of the sperm cells. Among the principal changes, are observed an increase of the plasma membrane fluidity through cholesterol depletion, which favor the relocation of proteins located in the sperm head and involved in oocyte interaction, together with an alkalinization of the cytoplasm and plasma membrane hyperpolarization. Intense protein phosphorylation, which include some proteins involved in flagellar beating, is observed on the sperm flagellum. pH_i, intracellular pH; Em, membrane potential; […], cytoplasmic ion concentrations; ↑, increase; ↓, decrease. Plain and broken arrows indicate a direct and indirect effect, respectively.