The sodium-proton exchangers sNHE and NHE1 control plasma membrane hyperpolarization in mouse sperm

Sperm capacitation is a complex process that takes place in the female reproductive tract and empowers mammalian sperm with the competence to fertilize an egg. It consists of an intricate cascade of events that can be mimicked in vitro through incubation in a medium containing essential components, such as bicarbonate, albumin, Ca²⁺, and energy substrates, among others. Genetic and pharmacological studies have underscored the unique significance of the K⁺ channel SLO3 in membrane potential hyperpolarization, as evidenced by the infertility of mice lacking its expression. Notably, two key molecular events, sperm hyperpolarization and intracellular alkalinization, are central to the capacitation process. SLO3 is activated by alkalinization. However, the molecular mechanisms responsible for intracellular alkalization and activation of SLO3 are not completely understood. In this study, we examined the impact of Na⁺/H⁺ exchangers (NHEs) on mouse sperm membrane hyperpolarization during capacitation. Pharmacological inhibition of the NHE1 blocked membrane hyperpolarization. A similar effect was observed in sperm deficient of the Ca²⁺ channel CatSper because of NHE1 not being activated by Ca²⁺. In addition, the sperm-specific NHE (sNHE) KO did not show membrane hyperpolarization upon capacitation or induction with cAMP analogs. Our results show that sNHE is dually modulated by cAMP and membrane hyperpolarization probably through its cyclic nucleotide-binding domain and the voltage-sensor motif, respectively. Together, sNHE and NHE1 provide the alkalinization need for SLO3 activation during capacitation.