- As the sperm cell experiences increased bicarbonate concentration, soluble adenylyl cyclase is activated by this increase in [HCO3-].
- Bicarbonate enters the cell by a Na+/HCO3- cotransporter, as evidenced by fulfillment of the following conditions modeled by Demarco et al.: (i) bicarbonate dependence (ii) electrogenicity (iii) sodium ion dependence (iv) blockage by stilbenes such as DIDS and SITS (v) ability to increase pH.
- Soluble adenylyl cyclase, located in the midpiece and flagellum, has garnered more attention in capacitation research than the nine other types of membrane-associated ACs (mACs) based on its preserved function within in vitro models.
- The activation of sAC within the capacitation process is integral, as Hess and colleagues found sperm lacking sAC were immobile and unable to fertilize eggs, even when supplied with cAMP molecules, whose presence is a downstream effect of sAC activation.
- Although their role remains unclear due to fewer investigations, mACs may aid in preventing spontaneous acrosome reactions (AR) by facilitating the initial increase in cAMP to initiate capacitation and inhibiting further cAMP production to prevent spontaneous AR. Fraser and colleagues suggest that blockage of the inhibition of cAMP production by adding pertussis toxin provides evidence of the involvement of mAC3 and a G-protein.