Membrane permeability changes during Rana oocyte maturation.

A transition from an open system to a closed one must occur during the complex process of meiotic maturation of the amphibian oocyte. Membrane permeability to urea in Rana oocytes following progesterone stimulation was determined, and the largest decrease was found to coincide with germinal vesicle breakdown. These findings suggest that the timing of the disappearance of membrane permeability correlates with developmental events that prepare the oocyte for a hostile environment.