Changes in the both inward current and conductance of membrane by the fertilization were observed using the one microelectrode voltage clamp(or switch clamp) technique. Unfertilized eggs and both 1- and 2-cell stage eggs after fertilization were do㎁ted from the superovulated mouse (ICR, more than 6 weeks old) treated with PMSG(pregnant mare serum gonadotropin, Sigma) and HCG(human chorionic gonadotropin, Sigma) and ㎁turally ㎃ted ones, respectively in this experiment. Membrane potential was held at -90㎷ and the voltage step was applied from -80㎷ to 50㎷ with interval of l0㎷ or 20㎷ for 300㎳. since both of amplitudes and time courses in the membrane currents were various according to the states of cells and clamping condition, results were presented by their averages±SEM(standard mean error)and ratios or percentages.
Inward currents began to appear in response to the step depolarization from -60㎷ and reached its maximum at -50㎷. However, since the potential was not clamped evenly duriug the voltage step, current-voltage(I-V) relationship might be positively shifted 10 or 20㎷. From the steady-state currents plotted in the I-V curve, outward rectification was markedly observed. Peak inward currents(i_(in)) at -50㎷ were -0.62±0.23㎁(n=4),-0.52±0.25㎁(n=5) and -0.37±0.25㎁(n=6), in the 1-cell stage, 2-cell stage fertilized eggs and in the unfertilized eggs, respectively. Pure inward current (difference between steady-state and peak, i_(in. pure)) were -1.01±0.23㎁, -0.69±0.43㎁ and -0.68±0.29㎁, respectively in the 1-cell stage fertilized eggs, unfertilized eggs and 2-cell stage fertilized eggs. These results suggested that the outward current in fertilized eggs of 2-cell stage was more increased than those in the unfertilized eggs. Pure inward currents in the all stages of eggs showed a similar fashion in the I-V relationship from -50㎷ to 50㎷ and reversal potential at 50㎷. Time constant of inactivation(τ) in the inward current was decreased as the membrane potential was depolarized in the unfertilized and 2-cell stage eggs but in the 1-cell stage eggs t was not likely to be affected significantly. Slope conductances were 14.2nS, 8.9n5 and 7.7nS in the 1-cell, 2-cell stage fertilized eggs and the unfertilized eggs, respectively. Membranes between two cells within a zona pellucida seem to be electrical-connected in the 2-cell stage eggs from the observation made in the analysis for the electronic spread and decay to the current stimuli.
Both of inward current and membrane conductance were increased after fertilization in the mouse eggs. Inward current seems to be carried by the same ion or through the same channels up to the 2-cell stage and ion that carried inward current was thought to play important function after fertilization in the mouse eggs.
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