When spermatozoa of Asterina pectinifera are treated with a solution of homologous egg jelly, besides undergoing the acrosome reaction, they begin to degrade their histones gradually. The degradation is most prominent with histone H1, almost 75% of which is degraded within one hour at 20°C. The jelly‐induced histone degradation, like the acrosome reaction, requires external Ca2+, prefers high pHs and is susceptible to Ca2+‐channel antagonists such as verapamil and diltiazem. Histone degradation is also induced by nigericin as well as monensin in normal seawater, but not in Ca2+‐free seawater. Calcium ionophore A23187, that greatly facilitates the monensin‐induced histone degradation, also induces histone degradation by itself, slightly in normal seawater and markedly in Ca2+‐enriched seawater. Concanavalin A inhibits the jelly‐induced histone degradation but not the jelly‐induced acrosome reaction. These results suggest that egg jelly induces the histone degradation by enhancing Ca2+‐influx via a Ca2+‐channel(s) and by increasing cytoplasmic pH, through a pathway which is closely related to, but not entirely the same as, the one leading to the acrosome reaction.

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