title: Role of calcium ions in the control of embryogenesis of Xenopus. Changes in the subcellular distribution of calcium in early cleavage embryos after treatment with the ionophore A23187.
abstract: Treatment of stage 5 Xenopus embryos with the ionophore A23187 for only 10 min, in the absence of extracellular Mg2+ and Ca2+, causes cortical contractions and a high incidence of abnormal embryos during subsequent development. Cation analysis shows that divalent ions are not lost from the embryos, but that Ca2+ is redistributed within the subcellular fractions. Ca2+ is probably released from yolk platelets and/or pigment granules by the action of A23187, [Ca2+] rises in the cytosol, and the mitochondria attempt to take up this free Ca2+. The mitochondria concomitantly undergo characteristic ultrastructural transformations, changing towards energized-twisted and energized-zigzag conformations. A23187 allows these changes to be demonstrated in situ. Extracellular divalent cations (10(-4) M) interfere with this intracellular action of A23187. Intracellular accumulation of Na+ (by treatment with ouabain) or Li+ also causes abnormal development, probably by promoting a release of Ca2+ from the mitochondria. It is suggested (a) that all these treatments cause a rise in [Ca2+]i which interferes with normal, integrated cell division, so causing, in turn, abnormal embryogenesis, (b) that levels of [Ca2+]i are of importance in regulating cleavage, (c) that the mitochondria could well have a function in regulating [Ca2+]i during embryogenesis in Xenopus, and (d) that vegetalizing agents may well act by promoting a rise in [Ca2+]i in specific cells in the amphibian embryo.
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000187:drug effects / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000648:ultrastructure; D010860:Pigments, Biological / Q000378:metabolism; D014981:Xenopus / Q000196:embryology*
chemical_list: D000900:Anti-Bacterial Agents; D010860:Pigments, Biological; D000001:Calcimycin; D008274:Magnesium; D002118:Calcium