Fertilization and early embryology: A cytosolic sperm factor triggers calcium oscillations and membrane hyperpolarizations in human oocytes

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Abstract
Intracellular free Ca2+ concentrations ([Ca2+]1) and membrane potentials were measured in mature human oocytes. Injection of cytosolic extracts made from human or hamster spermatozoa triggered oscillations in [Ca2+]1 in human oocytes similar to those described previously in mouse and hamster oocytes. In contrast, injection of carrier buffer caused no [Ca2+]1 increase and injection of Ca2+-containing solutions caused only a single [Ca2+]1 transient. Injection of human sperm extracts also triggered [Ca2+]1 oscillations in mature mouse oocytes. The [Ca2+]1 oscillations in human oocytes were accompained by hyperpolarizations in membrane potential. Perfusing oocytes with the sulphydry1 reagent thimerosal also caused oscillations in the free [Ca2+]1 concentration simultaneously with membrane potential hyperpolarizations. These data suggest that human oocytes possess a similar mechanism for generating [Ca2+]1 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.

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