Ion fluxes through the progesterone-activated channel of the sperm plasma membrane.
We have characterized ionic changes triggered by progesterone in human spermatozoa. This steroid, which is a fast-acting stimulator of the acrosome reaction, triggered a rapid increase in the cytoplasmic Ca2+ concentration ([Ca2+]i) which was entirely due to influx across the plasma membrane, as it was obliterated by chelation of extracellular Ca2+. Ca2+ fluxes were insensitive to verapamil and pertussis toxin, thus suggesting that they did not occur via voltage-gated channels and did not involve a pertussis toxin-sensitive G protein, and were potentiated in Na(+)-free, choline-containing or methylglucamine-containing medium. Progesterone also caused a depolarization of the plasma membrane in Na(+)-containing as well as in choline- or methyl-glucamine-containing saline; depolarization was larger in the absence of extracellular Ca2+, suggesting that Na+ and Ca2+ fluxes occurred through the same channel. Progesterone was able to trigger the acrosome reaction in the three media investigated (Na+, choline and methylglucamine), provided that extracellular Ca2+ was also present. We conclude that progesterone activates a membrane ion channel that is permeable to monovalent cations as well as to Ca2+.
Foresta
C
C
University of Padova, III Cattedra di Patologia Medica, Italy.
Rossato
M
M
Di Virgilio
F
F
D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials; D011374:Progesterone / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology
D007473:Ion Channels; D011374:Progesterone; D012964:Sodium; D002118:Calcium