OSCILLATIONS IN INTRACELLULAR FREE CALCIUM-INDUCED BY SPERMATOZOA IN HUMAN OOCYTES AT FERTILIZATION

Calcium has an important role in the events of egg activation and earl y preimplantation development. We investigated changes in intracellula r calcium concentration in human oocytes at fertilization using the ca lcium-sensitive photoprotein aequorin. Oocytes were donated for resear ch by patients undergoing in-vitro fertilization treatment in the Depa rtment of Obstetrics and Gynaecology. Cumulus cells, and in some cases zonae pellucidae, were removed by appropriate enzyme treatment. Singl e oocytes were micro-injected with aequorin and incubated in a chamber perfused with pre-equilibrated culture medium in a photomultiplier sy stem. Eleven zona-intact and 15 zona-free oocytes were incubated with sperm, and oocytes from each group were incubated without sperm as con trols. Dramatic transient increases in intracellular free calcium conc entration were recorded in three zona-intact and seven zona-free oocyt es, thought to be the first direct measurements of intracellular chang es in human oocytes at fertilization. The amplitude (up to 2.5 muM), d uration (120 s) and frequency (every 10-35 min) of these transients we re similar in zona-intact and zona-free oocytes. They resemble those r ecorded in mouse oocytes, which may therefore be a suitable model for biochemical events at human fertilization.