Fertilization signals a depolarization in X. laevis eggs. (A) Representative whole-cell recordings made during fertilization in control conditions (in MR/5 solution). Dashed line denotes 0 mV. (B) Images of X. laevis (top) egg before sperm addition and (bottom) egg ∼15 min after fertilization with animal pole contracted. Tukey box plot distributions of the (C) resting and fertilization potentials in control conditions and (D) depolarization rate (n = 31, recorded over 22 experiment days). The central line represents the median value, the box denotes the data spread from 25 and 75%, and the whiskers reflect 10–90%.