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Effects of aging on inositol 1,4,5‐triphosphate‐induced Ca 2+ release in unfertilized mouse oocytes
Author(s) -
Takahashi Toshifumi,
Saito Hidekazu,
Hiroi Masahiko,
Doi Katsuhiko,
Takahashi Eiji
Publication year - 2000
Publication title -
molecular reproduction and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 105
eISSN - 1098-2795
pISSN - 1040-452X
DOI - 10.1002/(sici)1098-2795(200003)55:3<299::aid-mrd8>3.0.co;2-g
Subject(s) - oocyte , thapsigargin , inositol , endoplasmic reticulum , biology , endocrinology , inositol trisphosphate , medicine , cytosol , oocyte activation , calcium , microbiology and biotechnology , biochemistry , receptor , enzyme , embryo
We previously demonstrated in the mouse oocyte that in vivo postovulatory aging significantly suppresses activity of the endoplasmic reticulum (ER) Ca 2+ ‐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 2+ release from the inositol 1,4,5‐triphosphate (InsP 3 )‐sensitive Ca 2+ channels of the ER membrane, because not only Ca 2+ reuptake, but also Ca 2+ release from the ER, substantially affect Ca 2+ oscillations in fertilized oocytes. A transient increase in cytosolic free Ca 2+ concentration ([Ca 2+ ] 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 2+ ] i significantly decreased in the aged oocytes. Reduced ER Ca 2+ release in the aged oocyte may not be attributable to aging‐related desensitization of the InsP 3 ‐sensitive Ca 2+ channels in the ER because concentrations of caged InsP 3 for half maximal [Ca 2+ ] i increase were identical for fresh and aged oocytes. The peak [Ca 2+ ] i response following administration of 5 μM thapsigargin, a specific ER Ca 2+ ‐ATPase inhibitor, was significantly reduced in the aged oocyte, suggesting reduction of the ER Ca 2+ stores. We conclude from these results that reduction of Ca 2+ release from the InsP 3 ‐sensitive Ca 2+ stores in the aged oocyte arises from depletion of the ER Ca 2+ stores with aging. These aging‐related changes in Ca 2+ release and reuptake may account for alterations in Ca 2+ oscillations in aged fertilized oocytes. Mol. Reprod. Dev. 55:299–306, 2000. © 2000 Wiley‐Liss, Inc.