Preimplantation embrology

Open Access

1 April 1996

journal article
research article
Published by Oxford University Press (OUP) in Molecular Human Reproduction

Vol. 2 (4) , 265-272
https://doi.org/10.1093/molehr/2.4.265

Abstract

This study was undertaken to localize ryanodine-sensitive Ca²⁺ stores in human oocytes and to evaluate their role in the Ca²⁺ oscillations responsible for oocyte activation at fertilization. The addition of ryanodine provoked a Ca²⁺ discharge from stores localized throughout the ooplasm with the exception of the cortical and subcortical peripheral regions. The ryanodine-induced discharge was typically followed by a short series of Ca²⁺ oscillations that only involved the cytoplasmic region populated by the ryanodine-sensitive stores. In contrast, the Ca²⁺ oscillations induced by the thiol reagent thimerosal or by spermatozoa at fertilization were of a much longer duration and also involved ryanodine-insensitive stores. Presumably, these ryanodine-insensitive stores are sensitive to inositol 1, 4, 5-trisphosphate (InsP3). The addition of ryanodine to oocytes during ongoing thimerosal- or sperm-induced Ca²⁺ oscillations inhibited the oscillations. These data suggest a co-operation between the ryanodine-sensitive and ryanodine-insensitive stores in maintaining the sperm-induced Ca²⁺ oscillations. In this two-store oscillation model, each periodic [Ca²⁺]i increase is triggered by a Ca²⁺ discharge from the peripheral, InsP₃-sensitive stores inducing Ca²⁺-induced Ca²⁺ release from the ryanodine-sensitive stores. However, the pacemaker frequency of the Ca²⁺ discharges from the InsP₃-sensitive stores is conditioned by the actual physiological state of the ryanodine-sensitive stores.

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