CHANGES OF THE MEMBRANE POTENTIAL AT THE TIME OF FERTILIZATION IN THE SEA URCHIN EGG WITH SPECIAL REFERENCE TO THE FERTILIZATION-WAVE

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Abstract
An experimental device was developed from the work of Uehara and Sugiyama (1969), in order to study the electrical phenomena accompanying the fertilization-wave in the sea urchin egg. The change in membrane potential upon fertilization consists of 2 peaks (Itoet al., 1970), being preceded by a shoulder. The shoulder appears within the "latent period" (Allen and Griffin, 1958), and the 2 peaks correspond to the breakdown of the cortical granules and the formation of the fertilization membrane. When the equatorial region of the egg surface was exposed to a detergent-sea water, the breakdown of the cortical granules and the formation of the fertilization membrane are induced only in this ring-shaped area. Sperm is then added to one of the polar regions. The fertilization-wave, starting from the point of sperm-entry, propagates across the detergent-treated region, and the membrane is formed on the whole egg surface. During such an experiment, changes of the membrane potential in the detergent-treated region were measured. 1 to 3 sudden transient depolarizations appear, followed by a delayed small depolarization. It is presumed that the initial depolarization corresponds to the fertilization-wave. The pattern of the potential change at normal fertilization may be explained by complexity of the cortical change, and the initial depolarizing shoulder is considered to correspond to the fertilization-wave, which is isolated by the above-mentioned device.

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