[Electrophysiological study of the frog egg at various stages of development. IV. Changes associated with the...

The I/V relationship of frog oocytes is markedly modified following maturation, lacking the mature unfertilized egg cell membrane of K-selective channels and the leakage being strongly reduced. The only kind of voltage-dependent channels still present in this membrane are activated by depolarizing steps to potentials more positive than 30-40 mV; the current flowing through these channels is carried at least partly by Na+. At difference with the immature oocyte, where several ionic mechanisms are oriented to maintain the membrane potential at a constant level, the mature egg-cell admits considerable voltage deflections. The observed variations in membrane properties could be of importance in allowing the maturation process and/or in preparing the mature egg-cell to successful fertilization.