Fertilization-signaled depolarization does not require Ca²⁺ entry into X. laevis eggs. (A and B) Representative fertilization recordings made in solutions with 10 µM GdCl₃ (A) and 20 µM SK&F-96365 (B). Dashed lines denote 0 mV. (C–E) Tukey box plot distributions of the resting (C) and fertilization (D) potentials and depolarization rate (E) for indicated treatments (n = 8–12, recorded over 3 experiment days per treatment). In D and E, the gray lines denote the Tukey box plot distributions for recordings made in control conditions (in the MR/5 solution), where the solid line represents the median value, the dashed lines denote the data spread from 25 and 75%, and the whiskers reflect 10–90%. (F) Images of X. laevis embryos from monospermic (top) and polyspermic (bottom) fertilizations. (G) Proportion of polyspermic embryos out of total developed embryos in control, Gd³⁺, and SK&F-96365 (n = 3–6, recorded over 3–6 experiment days per treatment, the mean values ± SEM are reported).