Changes in membrane properties during in-vitro meiotic maturation of the limpet Patella vulgata

Changes in the membrane properties of the oocyte of the mollusk, Patella vulgata, were analyzed following the induction of meiosis reinitiation by paleopedial ganglia extract or by the weak base ammonia. During maturation it was possible to distinguish between an early phase characterized by an initial hyperpolarization and a late phase consisting of a depolarization which triggers an action potential with a long-term overshoot (20 minutes) of the membrane potential. Major changes in individual ionic permeabilities were studied using both current and voltage clamp conditions. The depolarizing phase appears to depend on decreases in K+ membrane permeability. Finally we observed that the overshoot did not appear to be directly related to germinal vesicle breakdown (GVBD) since it was absent in Na-deprived artificial sea water and could be elicited in the presence of TEA bromide, which did not induce maturation. This last observation suggests that it may result from a change in specific K+ ion permeability due to the possible activation of stretch channels.