A cytoplasmic cell cycle controls the activity of a K + channel in pre‐implantation mouse embryos

We previously have reported that the activity of a 240 pS K + channel varies during the cell cycle in pre‐implantation mouse embryos. In the present study, we show that: (i) the cycling of channel activity is not prevented by inhibiting protein synthesis and hence does not involve cyclin‐dependent kinase 1 (cdk1)–cyclin B; and (ii) the cycling of channel activity continues in anucleate zygote fragments with a time course similar to that observed in nucleate fragments. We further demonstrate that: (i) persistent activation of the K + channel in one‐cell embryos arrested in metaphase requires the maintenance of an active cdk1–cyclin B complex; and (ii) both DNA synthesis inhibition with aphidicolin and DNA damage produced by mitomycin C prevent the down‐regulation of the channel at the start of S phase by a mechanism that requires tyrosine kinase activation. Thus, the 240 pS K + channel in these cells is controlled by a previously unsuspected cytoplasmic clock that functions independently of the well‐known clock controlling the chromosomal cell cycle, but can interact with it.