23 - Ion Channels in Sperm

Abstract

The interaction between gametes is a matter of life and death involving cell signaling and crucial participation of ion channels. The sea urchin has proved to be an excellent model with which to study reproduction. This chapter explores that 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. Sea urchin sperm are very tiny cells. This has precluded a characterization of their electrophysiological properties that shed light on the molecular mechanisms determining their fascinating egg induced behavioral changes. Two strategies are used to circumvent this problem: (1) model membranes formed from sperm components and patch-clamp techniques in whole cells are used to detect the activity of single channels in the plasma membrane of sea urchin sperm; and (2) sea urchin sperm are swollen in diluted seawater. Swollen sperm respond to speract, a decapeptide from the outer layer of the Strongylocentrotus purpuratus egg with changes in membrane potential, pH i , and [Ca] i , as normal cells do. Thus, swollen sperm provide new avenues for studying ionic channels and their regulation by egg factors and second messengers.