Figure 1. The fast block in X. laevis.

A) Schematic of a depolarization recorded during fertilization of an egg from the African clawed frog, Xenopus laevis. B) Signaling mechanisms of the fast block in X. laevis eggs. Fertilization in frog eggs signals activation of PLC, which cleaves phosphatidylinositol 4,5-bisphosphate (PIP₂) into IP₃ and diacylglycerol (DAG). IP₃ evokes Ca²⁺ release from the ER, and this Ca²⁺ opens the TMEM16A channel to induce Cl⁻ efflux and membrane depolarization. After a prolonged depolarization, the membrane potential repolarized back to rest via unknown ionic movement (adapted from Wozniak et al. 2018c).