Fig. 5.

IP₃R1 down-regulation during fertilization underlies the progressive increase in the interval between [Ca²⁺]_i spikes. In vitro fertilized mouse eggs cultured in the absence (left part) or presence (right part) of colcemid (100 ng/ml) were monitored for [Ca²⁺]_i responses starting ~90 min after insemination to minimize UV light exposure, which delays cell-cycle progression. Colcemid treatment avoided the abrupt termination of oscillations, although it did not prevent the growing gap between [Ca²⁺]_i rises (A). Under the same conditions, SrCl₂-induced oscillations exhibited broadening intervals between rises in the absence of colcemid, which was prevented by colcemid (B). The double head arrows in (A) and (B) connect horizontal bars that represent the length of the intervals between [Ca²⁺]_i rises, which changed during the course of oscillations in fertilized eggs treated with colcemid but that remained largely unchanged in SrCl₂-treated eggs in the presence of colcemid.