Inositol trisphosphate is required for the propagation of calcium waves in Xenopus oocytes.

Stimuli which act through the second messenger inositol 1,4,5-trisphosphate (InsP3) often increase free intracellular Ca2+ concentration ([Ca2+]i) in a localized subcellular area. Actively propagated Ca2+ waves then extend this focal Ca2+ signal to other parts of the cell. To understand how cells may control the spatial distribution of Ca2+, we investigated the mechanism by which Ca2+ waves propagate through the cytoplasm of Xenopus oocytes. Heparin, which inhibits the binding of InsP3 to its receptor, prevented the migration of Ca2+ waves induced by a poorly metabolized InsP3 (InsP3S3). This result suggested that Ca2+ waves move through the cell via the serial release of Ca2+ from InsP3-sensitive stores. Interventions which caused a localized increase in [Ca2+]i without elevations of InsP3 did not trigger Ca2+ waves. In the presence of a Ins-P3S3, however, endogenously released or locally injected Ca2+ elicited Ca2+ waves. A cooperative interaction between Ca2+ and InsP3 may therefore be responsible for the propagation of Ca2+ waves.