The Role of Sperm Ion Channels in Reproduction

Fertilization is a critical process that leads to the development of a new organism and secures survival of the species. Mammalian fertilization results in the fusion of male gamete, spermatozoon, with the female gamete, an ovum, and takes place in the ampulla-a specified region of the female reproductive tract. The ovulated egg arrives to the ampulla, where it awaits spermatozoa. However, the egg survival time is limited to 12. h, after which it disintegrates if not fertilized by the spermatozoon. To ensure the timely arrival, spermatozoa develop robust motility and overcome numerous obstacles presented by the female reproductive tract. The principle of sperm motility has fascinated researchers since this cell was first discovered in 1677 by Antonie van Leeuwenhoek. Spermatozoa are equipped with sophisticated molecular mechanisms that allow successful navigation in the female reproductive tract. To succeed, a spermatozoon must sense the environment and adapt its motility, which is controlled by adenosine triphosphate production and flagellar ion homeostasis, which in turn is under tight control of sperm ion channels and transporters. Sperm intracellular pH, membrane voltage, and intracellular calcium concentration are all important for sperm motility. Although all mammalian sperm are united in their goal to find and fertilize an egg, the molecular mechanisms they utilize for this purpose differ among species, especially on the level of ion channels. Despite advances in reproductive biology, approximately 80% of male infertility cases are idiopathic. This indicates our insufficient understanding of sophisticated machinery regulating human sperm physiology. Sperm ion channels are known to be important regulators of sperm physiology, and one of the most studied proteins to date is the calcium ion channel cation channels of sperm (CatSper), which is vital for fertility in both mice and humans. In this chapter we discuss the role of sperm ion channels in fertility with emphasis on CatSper and its regulation.