Involvement of zinc in the regulation of pHi, motility, and acrosome reactions in sea urchin sperm.

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Abstract
When sperm of Strongylocentrotus purpuratus of Lytechinus pictus are diluted into seawater, motility is initiated; and when exposed to egg jelly, an acrosome reaction is induced. In the presence of a variety of structurally different metal chelators (0.1-1 mM EDTA, EGTA, [ethyleneglycol bis [.beta.-aminoethylether]-N,N''-tetraacetic acid], phenanthroline, dipyridyl, cysteine, or dithiothreitol), motility initiation is delayed and the acrosome reaction is inhibited. Of the metals detected in the sperm of these 2 spp., very low levels of Zn2+ (0.1 .mu.M free Zn2+) uniquely prevent this chelator inhibition. L. pictus sperm concentrate 65Zn2+ from seawater, and EDTA removes 50% of the accumulated 65Zn2+ by 5 min. Since both sperm motility and acrosome reactions are in part regulated by intracellular pH (pHi), the effect of chelators on the sperm pHi was examined by using the fluorescent pH sensitive probe, 9-aminoacridine. EDTA depresses sperm pHi, in both species, and 0.1 .mu.M free Zn2+ reverses this phi depression. When sperm are diluted into media that contain chelators, both NH4Cl and monensin (a Na+/H+ ionophore) increase the sperm pHi and reverse the chelator inhibition of sperm motility and acrosome reactions. The results of this study are consistent with the involvement of a trace metal (probably Zn) in the pHi regulation of sea urchin sperm, and indicate a likely mechanism for the previously observed effects of chelators on sperm motility and acrosome reactions.