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Fig. 3. Increased cytoplasmic Ca²⁺-buffering does not prevent the first mitotic division. (A) Fertilized and parthenogenetic embryos were microinjected with BAPTA, Br₂BAPTA, EGTA (final concentrations 10 mM) or injection buffer, or were loaded with BAPTA-AM (10 µM) 1-2 hours before the predicted time of NEBD. Data are expressed as the percentage of embryos that had undergone NEBD within 20 hours of fertilization or parthenogenetic activation. Only BAPTA-AM treatment caused a significant inhibition of NEBD compared with controls (P<0.01, ² test). A minimum of two replicates were performed for each treatment. (B) One-cell embryos were microinjected with cIns(1,4,5)P₃ and BAPTA (final concentration 10 mM; n=18) or cIns(1,4,5)P₃ only (n=13). Injected embryos were loaded with Fura-red and [Ca²⁺]_i was monitored during 10 millisecond, 100 millisecond, 1000 millisecond and 3000 millisecond exposures of UV light at 2 minute intervals. The peak change in Fura-red emission ratio was significantly reduced by BAPTA in response to 100 millisecond (#, P<0.05), 1000 millisecond and 3000 millisecond exposures (^*, P<0.01). (C) BAPTA-injected embryos fail to exhibit repetitive Ca²⁺ transients in mitosis (n=19). Notice, however, that small fluctuations in Fura-2 baseline were detected at NEBD (ii, inset) (open arrow). Control embryos imaged at the same time exhibited characteristic Ca²⁺ oscillations (6.3±1.1 transients per embryo, n=14). No transients were detected following cytokinesis (closed arrow).

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