Evidence in support of the hypothesis of an electrically mediated fast block to polyspermy in sea urchin eggs.

Action currents were recorded extracellularly in sea urchin (Echinus esculentus and Psammechinus miliaris) eggs at fertilization. The action current was shown to correspond to the rising phase of a regenerative action potential by simultaneous intracellular recording. The uniform occurrence of such an action current at fertilization indicates that the resting potential of the unimpaled egg must be more negative than -50 mV, the action potential threshold, and offers confirmation of the hypothesis that the fast block to polyspermy in the sea urchin egg is electrical in nature.