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Intracellular levels of hydrogen peroxide and nitric oxide in oocytes at various stages of meiotic cell cycle and apoptosis
(2009) Anima Tripathi; Sabana Khatun; A.N. Pandey; S.K. Mishra; Radha Chaube; T.G. Shrivastav; S.K. Chaube
The objective was to find out the functional roles of hydrogen peroxide (H2O2) and nitric oxide (NO) during various stages of meiotic cell cycle and apoptosis in rat oocytes. For this purpose, 30 oocytes from each stage such as diplotene, metaphase-I (M-I), metaphase-II (M-II) and apoptosis were collected and intracellular H2O2, total nitrite level and inducible nitric oxide synthase (iNOS) expression were analysed. This study demonstrated that generation of a tonic level of H2O2 induces meiotic resumption in diplotene-arrested oocytes and further increase may lead to apoptosis. Conversely, reduction in iNOS expression and total nitrite level are associated with meiotic resumption in diplotene-arrested oocytes, but induce apoptosis in aged oocytes. These results suggest that generation of a tonic level of H2 O2, reduced iNOS expression and total nitrite level are associated with meiotic resumption, while more generation of H2O2 and sustained reduced total nitrite level are linked with oocyte apoptosis in rat.
Extracellular calcium protects against verapamil-induced metaphase-II arrest and initiation of apoptosis in aged rat eggs
(2009) S.K. Chaube; Anima Tripathi; Sabana Khatun; S.K. Mishra; P.V. Prasad; T.G. Shrivastav
Non-specific L-type calcium channel blockers, such as verapamil (≥50 μM), induce metaphase-II (M-II) arrest and apoptosis in aged rat eggs cultured in Ca2+-deficient medium. However, the effects of extracellular Ca2+ on verapamil-induced M-II arrest and apoptosis have not yet been reported. We have demonstrated that postovulatory aging induced exit from M-II arrest by extruding a second polar body, a morphological sign of spontaneous egg activation (SEA). Verapamil inhibited SEA and induced egg apoptosis in a dose-dependent manner in Ca2+-deficient medium. The initiation of apoptotic features was observed at 50 μM of verapamil. Extracellular Ca2+ (1.80 mM) reduced intracellular H2O2 level, bax protein expression, caspase-3 activity, DNA fragmentation and protected against 50 μM, but not higher concentrations of ≥100 μM in verapamil-induced egg apoptosis. These results suggest that extracellular Ca2+ ions have a role during SEA and protect against verapamil-induced apoptosis in aged rat eggs. © 2009 International Federation for Cell Biology.

2009

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