COMPARISON OF CA2+ RESPONSES IN HUMAN OOCYTES FERTILIZED BY SUBZONAL INSEMINATION AND BY INTRACYTOPLASMIC SPERM INJECTION

Objective: To evaluate the consequences of bypassing the normal intera ction between the sperm and oocyte surfaces for the form of Ca2+ respo nses developing in oocytes at fertilization. Design: Oocytes were fert ilized by subzonal insemination (SUZI) (maintaining the normal interac tion between cell surfaces of both gametes) or by direct intracytoplas mic sperm injection, and changes in intracellular free Ca2+ concentrat ion were evaluated by confocal laser scanning microscopy after loading oocytes with a fluorescent Ca2+ indicator. Setting: Private hospital, public research center, and university-based laboratory. Patients, Pa rticipants: Patients participating in an assisted reproduction program . Interventions: In vitro fertilization, SUZI, intracytoplasmic sperm injection.Main Outcome Measures: Changes in intracellular free Ca2+ co ncentration. Results: All oocytes fertilized after SUZI showed an osci llatory Ca2+ response introduced by a short initial phase with faster Ca2+ oscillations. In contrast, oocytes fertilized after intracytoplas mic sperm injection did not show a similar change in the oscillation r hythm. In both cases, Ca2+ increases were propagated throughout the oo plasm in a wave-like manner. Conclusions: The results show that there is a relationship between gamete surface contact and the form of Ca2fluxes accompanying fertilization. When the contact between gamete sur faces is skipped by direct sperm injection to the ooplasm, a delayed, truncated Ca2+ response is produced which, however, can maintain the f orm of Ca2+ waves and Ca2+ oscillations typical of normal fertilizatio n.