Source and sinks for the calcium released during fertilization of single sea urchin eggs.

Open Access
Publisher Website
Google Scholar
Abstract
The source and sinks for the intracellular Ca released during fertilization were examined in single eggs from the sea urchin, A. punctulata. Single eggs were microinjected with the Ca photoprotein, aequorin. The Ca-aequorin luminescence was measured with a microscope-photomultiplier or observed with a microscope-image intensifier-video system. In the normal egg a propagated release was observed. The source of the Ca was investigated in the organelle-stratified centrifuged egg and by the use of mitochondrial uncouplers. In the organelle-stratified centrifuged egg, the Ca-aequorin luminescence was found to originate from the clear zone. The principal constituent of the clear zone is the endoplasmic reticulum. Other potential sources of Ca are the mitochondria. Their contribution to the Ca transient was investigated by exposure of aequorin-injected eggs to mitochondrial uncouplers either before or after fertilization. There was no Ca released from the mitochondria before fertilization. A very large Ca store was released from the mitochondria after fertilization. Eggs fertilized in the presence of uncouplers showed no increase in the Ca-aequorin luminescence over untreated eggs. In the absence of mitochondrial uptake, other sinks for Ca with affinity and capacity similar to the mitochondria exist, but their nature is unknown. The endoplasmic reticulum is the source of the intracellular Ca released upon fertilization and that the mitochondria are the principal sink. The results are discussed with regard to the metabolic activation of the egg.