Effects of aging on inositol 1,4,5-triphosphate-induced Ca2+ release in unfertilized mouse oocytes
✍ Scribed by Toshifumi Takahashi; Hidekazu Saito; Masahiko Hiroi; Katsuhiko Doi; Eiji Takahashi
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 169 KB
- Volume
- 55
- Category
- Article
- ISSN
- 1040-452X
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✦ Synopsis
We previously demonstrated in the mouse oocyte that in vivo postovulatory aging significantly suppresses activity of the endoplasmic reticulum (ER) Ca 2ϩ -ATPase (Igarashi et al. 1997. Mol Reprod Dev 48:383-390). We undertook the present study to further examine the effects of oocyte aging on Ca 2ϩ release from the inositol 1,4,5-triphosphate (InsP 3 )sensitive Ca 2ϩ channels of the ER membrane, because not only Ca 2ϩ reuptake, but also Ca 2ϩ release from the ER, substantially affect Ca 2ϩ oscillations in fertilized oocytes. A transient increase in cytosolic free Ca 2ϩ concentration ([Ca 2ϩ ] i ) was induced by photolysis of caged InsP 3 microinjected into the cytoplasm in both fresh (14 hr post hCG) and aged (20 hr or 24 hr post hCG) oocytes, where the maximum rate of increase in [Ca 2ϩ ] i significantly decreased in the aged oocytes. Reduced ER Ca 2ϩ release in the aged oocyte may not be attributable to aging-related desensitization of the InsP 3sensitive Ca 2ϩ channels in the ER because concentrations of caged InsP 3 for half maximal [Ca 2ϩ ] i increase were identical for fresh and aged oocytes. The peak [Ca 2ϩ ] i response following administration of 5 M thapsigargin, a specific ER Ca 2ϩ -ATPase inhibitor, was significantly reduced in the aged oocyte, suggesting reduction of the ER Ca 2ϩ stores. We conclude from these results that reduction of Ca 2ϩ release from the InsP 3 -sensitive Ca 2ϩ stores in the aged oocyte arises from depletion of the ER Ca 2ϩ stores with aging. These aging-related changes in Ca 2ϩ release and reuptake may account for alterations in Ca 2ϩ oscillations in aged fertilized oocytes.