Figure 7.

InsP₃-induced Ca²⁺ release is reduced in oocytes that have extruded the second polar body. Oocytes were injected with 50 μM cInsP₃ and loaded with Fura red to monitor Ca²⁺ in response to a series of InsP₃ concentrations. Injection of 50 μM cInsP₃ provides a reservoir of InsP₃ that is not significantly depleted by repeated photolysis events of 1000 ms every 2 min (A). InsP₃ was photoreleased in MII oocytes and ethanol-activated parthenogenetic embryos at the Pb2 and Pn stages. The amount of InsP₃ released, as measured by the change in Fura red ratio, was controlled by changing the duration of UV light from 10 to 3000 ms. MII oocytes release more Ca²⁺ for a given dose of InsP₃ than those that have been activated (B). Release of Ca²⁺ in aged and fresh oocytes is similar, suggesting time from ovulation does not unduly affect the amount of Ca²⁺ released (C). Difference in amount of Ca²⁺ released in response to InsP₃ was not due to oocyte aging.