A cytosolic sperm factor triggers calcium oscillations and membrane hyperpolarizations in human oocytes.
Intracellular free Ca2+ concentrations ([Ca2+]i) and membrane potentials were measured in mature human oocytes. Injection of cytosolic extracts made from human or hamster spermatozoa triggered oscillations in [Ca2+]i in human oocytes similar to those described previously in mouse and hamster oocytes. In contrast, injection of carrier buffer caused no [Ca2+]i increase and injection of Ca(2+)-containing solutions caused only a single [Ca2+]i transient. Injection of human sperm extracts also triggered [Ca2+]i oscillations in mature mouse oocytes. The [Ca2+]i oscillations in human oocytes were accompanied by hyperpolarizations in membrane potential. Perfusing oocytes with the sulphydryl reagent thimerosal also caused oscillations in the free [Ca2+]i concentration simultaneously with membrane potential hyperpolarizations. These data suggest that human oocytes possess a similar mechanism for generating [Ca2+]i oscillations to those described in other mammalian oocytes and a membrane potential response similar to that seen previously specifically in hamster oocytes. The data also support the view that human oocytes are activated at fertilization by diffusion of a protein from the spermatozoa into the ooplasm after gamete membrane fusion.
Homa
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Portland Hospital Fertility Unit, BMI Portland Hospital for Women and Children, London, UK.
Swann
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D000818:Animals; D001683:Biological Clocks / Q000187:drug effects*; D001685:Biological Factors / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D006224:Cricetinae; D003600:Cytosol / Q000737:chemistry*; D005260:Female; D006801:Humans; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009865:Oocytes / Q000187:drug effects* / Q000378:metabolism; D013045:Species Specificity; D013094:Spermatozoa / Q000737:chemistry* / Q000648:ultrastructure; D013849:Thimerosal / Q000494:pharmacology
D001685:Biological Factors; D013849:Thimerosal; D002118:Calcium