A fast transient hyperpolarization occurs during the sea urchin sperm acrosome reaction induced by egg jelly

Abstract

The egg jelly-induced sea urchin sperm depolarization, assayed with the membrane potential-sensitive dye diS-C₃-(5), is preceded by a fast quenching, which was initially taken as an artifact. Here we show that part of this quenching results from a K⁺ -dependent transient hyperpolarization (∼4 s). Seawater containing 25–35 mM KCl inhibits this hyperpolarization, the depolarization and the acrosome reaction induced by egg jelly, or by the acrosome reaction inducing factor purified therefrom. These results suggest that egg jelly induces a transient hyperpolarization mediated by an increase in K⁺ permeability, which may be involved in triggering the acrosome reaction