Ca2+ entry through store-operated channels in mouse sperm is initiated by egg ZP3 and drives the acrosome reaction

Fertilization occurs after the completion of the sperm acrosome reaction, a secretory event that is triggered during gamete adhesion. ZP3, an egg zona pellucida glycoprotein, produces a sustained increase of the internal Ca2+ concentration in mouse sperm, leading to acrosome reactions. Here rye show that the sustained Ca2+ concentration increase is due to the persistent activation of a Ca2+. influx mechanism during the late stages of ZP3 signal transduction. These cells also possess a Ca2+ store depletion-activated Ca2+ entry pathway that is open after treatment with thapsigargin. Thapsigargin and ZP3 activate the same Ca2+ permeation mechanism, as demonstrated by fluorescence quenching experiments and by channel antagonists. These studies show that ZP3 generates a sustained Ca2+ influx through a store depletion-operated pathway and that this drives the exocytotic acrosome reaction.