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

Abstract

Parthenogenetic activation of Lytechinus pictus eggs can be monitored after injection 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 Ca 2+ from intracellular stores. Ionophore and urea solutions release Ca 2+ 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 2+ from a different intracellular store. Treatment with the weak base NH 4Cl did not release intracellular Ca 2+ but did result in a momentary Ca 2+ influx if Ca 2+ was present in the external solution. Ca 2+ influx was not required for ammonia activation.