抄録
Calcium ionophore, A23187, induced a large depolarization of the membrane (referred to as the activation potential) of sea urchin Pseudocen-trotus depressus eggs, which was very similar to the fertilization potential induc-ed by a sperm. The egg membrane abruptly overshot to +12 mV, then slightly fell, and again slowly polarized to about +10 mV, where the membrane sustain-ed for about 10 sec. Peak values of this second component were found to be very sensitive to the external Na+ concentration and external K+ concentration. These features were very similar to the second component (component B) of the fertilization potential. On the other hand, even when removed Ca2+ from exter-nal artificial sea water, the activation potential was found to show essentially the same time course and magnitude as those in Ca2+ -containing artificial sea water. Thus the second component of the activation potential elicited by A23187 is probably induced by the increment of Na+ and K+ permeabilities, which might be triggered by the release of Ca2+ from the intracellular storing sites. These results suggest that component B of the fertilization potential is caused by the elevation of internal Ca2+ concentration.
