Free calcium in Xenopus embryos measured with ion-selective microelectrodes

A regulatory role for intracellular free calcium has been suggested in cell division¹ and intercellular communication via gap junctions^2,3. Previous measurements of cytoplasmic free Ca²⁺ during cell division and uncoupling have been made with the Ca²⁺-sensitive photoprotein aequorin^4,5. We now report experiments using Ca²⁺-sensitive microelectrodes to monitor free Ca²⁺ in the cells and intercellular fluid of early embryos of the amphibian Xenopus laevis. In addition to measuring basal levels, we have looked for changes in free Ca²⁺ during cell division and during electrical uncoupling of the normally coupled embryonic cells, induced by acidification of the intracellular medium^5-7.