Fertilization Membrane Formation in Sea Urchin Eggs Induced by Drugs Known to Cause Ca²⁺Release from Isolated Sarcoplasmic Reticulum

<jats:p>Ryanodine, miconazole, clotrimazole, doxorubicin, quercetin, halothane, caffeine and chloroform, which activate Ca<jats:sup>2+</jats:sup>‐induced Ca<jats:sup>2+</jats:sup>release from Ca<jats:sup>2+</jats:sup>stores, induced Ca<jats:sup>2+</jats:sup>release from a particulate fraction isolated from sea urchin eggs, Ca<jats:sup>2+</jats:sup>influx into eggs and formation of a fertilization membrane in an appreciable number of eggs. Their minimum effective concentrations for inducing a fertilization membrane increased in the order of these drugs listed above, and this order was also the same as that of their minimum effective concentrations for inducing Ca<jats:sup>2+</jats:sup>release from the isolated particulate fraction. Their effect in inducing a fertilization membrane was blocked by ruthenium red and procaine, which inhibit Ca<jats:sup>2+</jats:sup>release from Ca<jats:sup>2+</jats:sup>stores. Thus these drugs probably induced sufficient Ca<jats:sup>2+</jats:sup>release to make the cytosolic Ca<jats:sup>2+</jats:sup>level high enough in many eggs for formation of a fertilization membrane. In the absence of external Ca<jats:sup>2+</jats:sup>, fewer eggs treated with these drugs formed a fertilization membrane and more eggs did so on further treatment with either A23187 or carbonylcyanide‐p‐trifluoromethoxy‐phenylhydrazone (FCCP). Thus, a high level of Ca<jats:sup>2+</jats:sup>is probably derived from Ca<jats:sup>2+</jats:sup>release through Ca<jats:sup>2+</jats:sup>releasing channels (by A23187), from mitochondria (by FCCP) and its transport from the external medium.</jats:p>