Membrane Potentials in Frog Eggs Fertilization of a frog oocyte by a sperm cell triggers ionic changes similar to those observed in neurons (during movement of the action potential) and initiates the events that result in cell division and development of the embryo. Oocytes can be stimulated to divide without fertilization by suspending them in 80 mM KCl (normal pond water contains 9 mM KCI). (a) Calculate how much the change in extracellular [KCI] changes the resting membrane potential of the oocyte. (Hint: Assume the oocyte contains 120 mM K+ and is permeable only to K+.) Assume a temperature of 20 C. (b) When the experiment is repeated in Ca+-free water, elevated [KCI] has no effect. What does this suggest about the mechanism of the KCl effect?