Figure 8.

Proposed model for the HCO₃⁻ transport during human sperm capacitation. An initial HCO₃⁻ influx through electrogenic NBC causes the stimulation of ADCY10, resulting in cAMP production and activation of PKA. Then PKA activity is necessary to phosphorylate and activate CFTR. Activation of CFTR results in sustained HCO₃⁻ influx and closing of ENaC. ENaC consequently contributes to the regulation of Em during capacitation together with SLO channels (SLO1 and/or SLO3). In the case of SLO3, its activity may be modulated by PKA as previously proposed in mouse sperm, although this possibility remains to be explored.