Differential Effects of the Egg Jelly Molecules FSG and SAP-I on Elevation of Intracellular Ca2+ and pH in Sea Urchin Spermatozoa

We examined the effects of two egg jelly components, a fucose sulfate glycoconjugate (FSG) and sperm-activating peptide I (SAP-I: Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly), on the intracellular pH (pH_i) and Ca²⁺ (Ca²⁺]_i) of spermatozoa of the sea urchin Hemicentrotus pulcherrimus . FSG and/or SAP-I induced elevations of Ca²⁺]; and pH_i in the spermatozoa at pH 8.0. At pH 8.0, a second addition of FSG did not induced further elevation of the Ca²⁺]_i or pH_i of spermatozoa treated with FSG, but addition or FSG after SAP-I or of SAP-I after FSG induced further increases of Ca²⁺]_i and pH_i, At pH 6.6, FSG and/or SAP-I did not induce significant elevation of the Ca²⁺]_i, although SAP-I elevated the pH_i, its half-maximal effective concentration being 10 to 100 pM. At pH 8.0, tetraethyl-ammonium, a voltage-sensitive K⁺-channel blocker, inhibited induction of the acrosome reaction and elevations of Ca²⁺]_i and pH_i by FSG, but did not affect those by SAP-I. These results suggest that FSG and SAP-I activate different Ca²⁺ and H⁺ transport systems.