30 - Ion Channels in Sperm

Abstract

This chapter discusses the ion channels in sperm. The chapter mentions that the flow of ions through the plasma membrane of sperm, particularly Ca2+, participates crucially in the events leading to fertilization. Cell communication involves molecular mechanisms as they play a key role in determining the behavior of organisms. The chapter discusses sperm responses to egg components and sperm ion channels. Sperm responses to egg components discuss sea urchin sperm, and mammalian sperm. Sperm ion channels discuss sea urchin sperm ion channels, and ion channels of mammalian sperm. Sea urchin sperm further discusses responses to egg peptides and acrosome reaction. Capacitation and acrosome reaction are also discussed under mammalian sperm. It is mentioned that mammalian sperm capacitation can be accomplished in vitro by incubating ejaculated sperm in defined medium. The three key components required for mammalian sperm capacitation in mouse sperm are Ca2+, NaHCO3, and serum albumin. Successful gamete interactions that require cell signaling and the crucial participation of ion channels determine the propagation of life. Ionic fluxes play a fundamental role in activation of respiration and motility, chemotaxis, the sperm acrosome reaction (AR), and therefore in fertilization. Sperm are excitable cells that quickly respond to components from the outer layer of the egg, the jelly, with fast changes in their plasma membrane permeability. Model membranes formed from sperm components and patch-clamp techniques in whole cells have been used to detect, for the first time, the activity of single channels in the plasma membrane of sea urchin and mouse sperm. Swollen sperm can be much more easily patch-clamped than normal sperm, thus, providing new avenues to study ionic channels and their regulation by egg factors and second messengers. An alternative to identifying and functionally studying ion channels in sperm is to look for their expression in spermatogenic cells, combining molecular biological strategies and electrophysiology. This will allow a deeper understanding of the finely arranged events that lead to sperm activation, induction of the acrosome reaction, and in the end to the generation of a new individual.