The role of Hv1 and CatSper channels in sperm activation

Elevations of sperm intracellular pH and Ca²⁺ regulate sperm motility, chemotaxis, capacitation and the acrosome reaction, and play a vital role in the ability of the sperm cell to reach and fertilise the egg. In human spermatozoa, the flagellar voltage-gated proton channel Hv1 is the main H⁺ extrusion pathway that controls sperm intracellular pH, and the pH-dependent flagellar Ca²⁺ channel CatSper is the main pathway for Ca²⁺ entry as measured by the whole-cell patch clamp technique. Hv1 and CatSper channels are co-localized within the principal piece of the sperm flagellum. Hv1 is dedicated to proton extrusion from flagellum and is activated by membrane depolarisation, an alkaline extracellular environment, the endocannabinoid anandamide, and removal of extracellular zinc, a potent Hv1 blocker. The CatSper channel is strongly potentiated by intracellular alkalinisation. Since Hv1 and CatSper channels are located in the same subcellular domain, proton extrusion via Hv1 channels should induce intraflagellar alkalinisation and activate CatSper ion channels. Therefore the combined action of Hv1 and CatSper channels in human spermatozoa can induce elevation of both intracellular pH and Ca²⁺ required for sperm activation in the female reproductive tract. Here, we discuss how Hv1 and CatSper channels regulate human sperm physiology and the differences in control of sperm intracellular pH and Ca²⁺ between species.