Figure 4.

A model describing the biochemical cascade in sperm capacitation: intracellular HCO₃− activates sAC to generate cAMP leading to PKA activation and cholesterol efflux from the sperm plasma membrane which further stimulate the HCO₃−/sAC/cAMP/PKA cascade. PKA activates Src to phosphorylate/inactivate PIP₂-bound gelsolin. PIP2 is a cofactor for PLD activation and this activation is stimulated by PKCα, leading to phosphatidylcholine hydrolysis and production of phosphatidic acid (PA) which mediates the conversion of G-actin to F-actin. Thus, activation of PLD and prevention of F-actin dispersion by inhibiting gelsolin, allows F-actin formation. F-actin in the head prevents immature acrosome reaction and in the tail F-actin regulates sperm motility including HA motility.