Fertilization Membrane Formation in Sea Urchin Eggs Induced by Drugs Known to Cause Ca

Ryanodine, miconazole, clotrimazole, doxorubicin, quercetin, halothane, caffeine and chloroform, which activate Ca2+ -induced Ca2+ release from Ca2+ stores, induced Ca2+ release from a particulate fraction isolated from sea urchin eggs, Ca2+ 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 Ca2+ release from the isolated particulate fraction. Their effect in inducing a fertilization membrane was blocked by ruthenium red and procaine, which inhibit Ca2+ release from Ca2+ stores. Thus these drugs probably induced sufficient Ca2+ release to make the cytosolic Ca2+ level high enough in many eggs for formation of a fertilization membrane. In the absence of external Ca2+ , 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 Ca2+ is probably derived from Ca2+ release through Ca2+ releasing channels (by A23187), from mitochondria (by FCCP) and its transport from the external medium.