Intracellular calcium release and the mechanisms of parthenogenetic activation of the sea urchin egg.

Parthenogenetic activation of Lytechinuspictus eggs can be monitored after inje&ion with the Ca-sensitive photoprotein aequorin to estimate calcium release during activation. Parthenogenetic treatments, including the nonelectrolyte urea, hypertonic sea water, and ionophore A23187, all acted to release Ca2+ from intracellular stores. Ionophore and urea solutions release Ca*’ from the same intracellular store as normal fertilization. This intracellular store can be reloaded after 40 min and discharged again. Hypertonic medium appears to release Ca” from a different intracelhtlar store. Treatment with the weak base NH&l did not release intracellular Ca2+ but did result in a momentary Ca2+ Influx if Ca2+ was present in the external solution. Ca*’ influx was not required for ammonia activation.