The cation channels of sperm also known as Catsper channels or CatSper, are ion channels that are related to the two-pore channels and distantly related to TRP channels. The four members of this family form voltage-gated Ca2+ channels that seem to be specific to sperm. As sperm encounter the more alkaline environment of the female reproductive tract, CatSper channels become activated by the altered ion concentration. These channels are required for proper fertilization. The study of these channels has been slow because they do not traffic to the cell membrane in many heterologous systems.
There are several factors that can activate the CatSper calcium channel, depending on species. In the mouse, channel is activated by progesterone released by the oocyte. The human CatSper channel is pH-sensitive, and requires a high-pH environment.  CatSper plays a key role in mediating hyperactive motility – prior to fertilization, sperm become entrapped within the fingerlike projections of the microvilli of the oviduct. In order for the sperm to fertilize the oocyte, CatSper must be present in order to initiate hyperactive motility, allowing the sperm to escape the microvilli and reach the oocyte for fertilization. 
Of the four members of the Catsper family, Catsper1 is found in the primary piece of sperm. Catsper1 plays an important role in evoked Ca2+ entry and regulation of hyperactivation in sperm. Catsper2 is localized in the sperm tail and is responsible for regulation of hyperactivation. Catsper3 and Catsper4 are found in both, the testes and sperm and play an important role in the motility of hyperactivated sperm. Although Catsper seems to play an important role in sperm function, Catspers1-4 null mice have been found to have normal testicular histology, sperm counts and morphology, which is indicative of normal progression of spermatogenesis. 
^Sun, Xiang-Hong, et al. “The Catsper Channel and Its Roles in Male Fertility: a Systematic Review.” Reproductive Biology and Endocrinology, vol. 15, no. 1, 2017, doi:10.1186/s12958-017-0281-2
^Carlson, Anne E., et al. “CatSper1 Required for Evoked Ca2+ Entry and Control of Flagellar Function in Sperm.” PNAS, National Academy of Sciences, 9 Dec. 2003, www.pnas.org/content/100/25/14864.short.
^Eun Hwa Park, Do Rim Kim, Ha Young Kim, Seong Kyu Park, and Mun Seog Chang. Panax ginseng induces the expression of CatSper genes and sperm hyper activation. Asian journal of andrology 2014;16(6):845-851.