Temporal and spatial dynamics of the periodic increase in intracellular free calcium at fertilization of golden hamster eggs

A series of periodic increases in intracellular free calcium concentration ([Ca 2+] i) occurred upon fertilization in golden hamster eggs. The spatial distribution of the Ca 2+ transients was investigated in single zona-free, aequorin-injected eggs, inseminated by single sperm. A supersensitive TV camera system for recording Ca 2+-aequorin luminescence enabled us to observe the spatial distribution of the Ca 2+ rise. In the first response, which usually occurred 10–30 sec after the sperm attachment, the increase in [Ca 2+] i began near the sperm attachment site, and the Ca 2+ rise spread over the entire egg within 4–7 sec. The Ca 2+ rise attained its peak in 5–8 sec, declined with almost even distribution, and ceased in 12–17 sec. The spreading Ca 2+ rise was repeated in the second and sometimes the third response, starting from the same focus, but spreading more rapidly (∼2 sec). In succeeding responses [Ca 2+] i increased synchronously in the whole cytoplasm within 1 sec. When additional sperm attached to the egg after the occurrence of the first response by the first sperm, the spread of the Ca 2+ rise could take place from near the site of additional sperm attachment but only in the second or third response.