Molecular Human Reproduction, Vol. 8, No. 10, 912-918,
October 2002
© 2002 European Society of Human Reproduction and Embryology
Ovary and oogenesis |
Inositol 1,4,5-trisphosphate receptor function in human oocytes: calcium responses and oocyte activation-related phenomena induced by photolytic release of InsP3 are blocked by a specific antibody to the type I receptor*
1 Infertility Centre, Department of Obstetrics and Gynaecology, 2 Department of Physiology and Pathophysiology, Faculty of Medicine, Ghent University, 3 Laboratory of Biochemistry and Molecular Cytology, Faculty of Agriculture, Ghent University, Ghent, Belgium, 4 Laboratory for Developmental Neurobiology, Brain Science Institute, RIKEN, Wako, Japan, 5 Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology and 6 Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan, USA
Type I inositol 1,4,5-trisphosphate-sensitive receptors (InsP3R) are expressed in human oocytes and may be involved in operating the Ca2+ release triggered by the fertilizing sperm. This study examines the contribution of type I InsP3R in operating Ca2+ release in human oocytes secondary to InsP3 itself, using a specific function-blocking antibody in conjunction with photolytic release of microinjected InsP3. Intracellular Ca2+ responses were assessed in oocytes microinjected with only caged InsP3 in experiment set A, while in experiment sets B and C, sibling oocytes were injected with caged InsP3 and the blocking antibody or a corresponding volume of medium, prior to flash photolysis. In experiment set C, certain fertilization-related phenomena (cortical granule exocytosis and chromatin configurations) were assessed using optical sections and three-dimensional image reconstructions obtained from a confocal laser scanning microscope. In experiment set A, photolytic release of InsP3 triggered a Ca2+ response (increase from 
100 to 220 nmol/l followed by an exponential recovery, n = 8) and a wave in the oocytes that spread from the stimulation point to the opposite pole. In set B, photolytic InsP3 release generated Ca2+ responses in control oocytes (n = 9), but not in the antibody-injected oocytes (n = 7). In set C, cortical granule exocytosis and anaphase chromosome configurations were noted in the control oocytes after flash photolysis (n = 6). These changes were completely absent in antibody injected oocytes as their cortical granules were intact and the chromosomes were in metaphase. These oocytes had also lacked Ca2+ responses as in set B (n = 5). This study demonstrates the functional presence of type I InsP3R-operated Ca2+ channels in human oocytes and further suggests an active role of InsP3 in triggering the Ca2+ rise and secondary activation phenomena at fertilization.
Ca2+ transients/caged IP3/fertilization/flash photolysis/inositol 1,4,5-trisphosphate receptors
* Presented at the 56th Annual Meeting of the American Society for Reproductive Medicine, San Diego, CA, USA in October 2000.
7 To whom correspondence should be addressed: Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, Wayne State University School of Medicine, 4707 St Antoine Boulevard, Detroit, MI 48201, USA. E-mail: pgoud{at}med.wayne.edu
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