Progesterone triggers a wave of increased free calcium during the human sperm acrosome reaction.
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.
Meizel
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S
Department of Cell Biology and Human Anatomy, School of Medicine, University of California, Davis 95616, USA.
Turner
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Nuccitelli
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D000177:Acrosome / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D005260:Female; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D008297:Male; D018715:Microscopy, Video; D010852:Picrotoxin / Q000494:pharmacology; D011374:Progesterone / Q000494:pharmacology*; D011963:Receptors, GABA-A / Q000502:physiology; D013075:Sperm Capacitation; D013084:Sperm-Ovum Interactions; D013997:Time Factors
D002118:Calcium; D005456:Fluorescent Dyes; D016257:Fura-2; D010852:Picrotoxin; D011374:Progesterone; D011963:Receptors, GABA-A