PROPIONATE AND CYCLOHEXIMIDE REVERSIBLY BLOCK PROGESTERONE INDUCED CALCIUM SURGE IN AMBYSTOMA MEXICANUM OOCYTES

The protoprotein aequorin was used in order to monitor Ca²⁺ transients in conditions where progesterone induced maturation was reversibly inhibited. Propionate but not isethionate Cl-free medium impaired both meiosis reinitiation and the Ca²⁺ transient, unless oocytes were returned to normal Cl-containing medium. Similar results were obtained with the protein synthesis inhibitor cycloheximide. In both cases, the incidence of germinal vesicle breakdown (GVBD) and the time schedule relating it to the Ca²⁺ surge appeared not very different from that found from control oocytes. The evidence suggests that both treatments act on the initial step by which progesterone triggers the intracellular Ca²⁺ release needed for maturation promoting factor (MPF) elaboration. No definitive conclusion can be reached however from these experiments concerning the need for protein synthesis during meiosis reinitiation.