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Dev Biol. 1997 Feb 1;182(1):67-75.

Progesterone triggers a wave of increased free calcium during the human sperm acrosome reaction.

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Department of Cell Biology and Human Anatomy, School of Medicine, University of California, Davis 95616, USA.


The mammalian sperm acrosome reaction (AR), an essential fertilization event, requires an influx of Ca2+. The Ca2+ increase occurring in the human sperm head during the AR initiated by progesterone, a putative in vivo AR initiator, was investigated using video-image analysis with fura-2, a fluorescent Ca2+ probe. Progesterone treatment of capacitated human sperm resulted in a wave-like increase in sperm head cytosolic [Ca2+]i that appears to increase fastest in a region near the equatorial segment and then spreads throughout the rest of the head. The progesterone-mediated Ca2+ increase in the sperm head was strongly inhibited and the wave eliminated by picrotoxin, a blocker of GABAA receptor/Cl- channels and an inhibitor of the progesterone-mediated Cl- efflux and progesterone-initiated AR of human sperm. These results are the first to detect a ligand-mediated Ca2+ wave in sperm and to suggest that Cl- efflux influences Ca2+ influx during the AR.

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