The apparent change in the egg membrane potential at fertilization gives rise to fertilization potential (FP). FP is the initial, transient electrical block to polyspermy as shown in most species especially those exhibiting external fertilization, and it protects the egg from a second sperm entry until the permanent, mechanical block is set up. | Turk J Biol 25 (2001) 277-289 © TÜB‹TAK Effects of Cd2+, Zn2+, Li+ and Al3+ on the Fertilization-Induced Membrane Potential Changes in the Egg of the Frog Rana cameranoi fieref ERDO⁄AN, Gülay LO⁄O⁄LU, Kerem Tuncay ÖZGÜNEN, Tuncay ÖZGÜNEN Çukurova University, Faculty of Medicine, Department of Physiology, 01330 Balcal›, Adana - TURKEY Received: Abstract: The apparent change in the egg membrane potential at fertilization gives rise to fertilization potential (FP). FP is the initial, transient electrical block to polyspermy as shown in most species especially those exhibiting external fertilization, and it protects the egg from a second sperm entry until the permanent, mechanical block is set up. Polyspermy risk is increased when this effective electrical block cannot reach a certain peak value or when it is of short duration. On the other hand, metal accumulation in the external environment is potentially toxic to living beings, and we aimed in the present study to evaluate the toxic effects of Cd2+, Zn2+, Li+ and Al3+ on the potential changes triggered by fertilization in the egg of the frog, Rana cameranoi. Egg membrane potentials were recorded using the conventional microelectrode technique. Resting membrane potential before fertilization and FP parameters were determined. Ten percent Ringer solution (pH=) was used as a control, and experimental groups were established by adding CdCl2 (68 µM), ZnCl2 (300 µM), LiCl ( mM) or AlCl3 ( mM) into this solution and adjusting their pHs to . Evaluation of our results revealed that duration of potential change induced by fertilization was significantly reduced by Li+ and Al3+ whereas Cd2+ prolonged the duration of FP (, Table). Peak Fertilization Potential (FPp): In the control group, sudden depolarization induced by fertilization reached ± mV; this value was significantly more positive in the group exposed to Zn2+ (± mV; p<) (Table, Fig. 3B). It did not change evidently
