FIGURE 4.

Schematic representation of some of the identified sperm membrane transporters involved in ion fluxes during human sperm capacitation. Cholesterol depletion occurring during capacitation also increases membrane fluidity. A panoply of ion transporters is involved in the complex ion fluxes, which induce membrane hyperpolarization, cytoplasm alkalinization and protein hyperphosphorylation. Slo13, sperm-specific K⁺ channel; ENaC, epithelial Na⁺ channel; CFTR, cystic fibrosis transmembrane conductance channel; SLC26, solute carrier 26; NBC, sodium HCO₃^– transporter; CatSPER, sperm specific Ca²⁺ channel; Hv1, proton channel; NHE, Na⁺/H⁺ exchanger; CA, carbonic anhydrases; pH_i, intracellular pH; Em, membrane potential; […], cytoplasmic ion concentrations; ↑, increase; ↓, decrease. Plain and broken arrows indicate a direct and indirect effect, respectively. CFTR stimulation by SLC26 proteins is represented by an arrow with (+) and ENaC inhibition by CFTR is represented by an arrow with (–).