Ca2+Entry through Store-operated Channels in Mouse Sperm Is Initiated by Egg ZP3 and Drives the Acrosome Reaction

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Abstract
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 we 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.