The effect of calcium upon embryonic growth was studied using cultured mouse preimplantation embryos. Both morphological development of the embryos and embryo DNA synthesis were shown to be dependent on the in the medium in which the embryos were grown. Reduction of the calcium concentration completely blocked cell division and blastocyst formation in the cultured embryos, but only moderately inhibited embryo DNA synthesis. Trifluoperazine, a calmodulin antagonist, strongly inhibited the calcium - dependent DNA synthesis in the embryos. On the other hand, the drug only slightly affected the morphological development of the embryos. These results demonstrate that calcium independently affects two different aspects of the embryo development, i.e. DNA synthesis and cell division. It is suggested that the former effect is calmodulin-dependent, while the latter involves the calcium-dependence of metabolite transport through the cell membranes.
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