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 (pHi) and Ca2+ ([Ca2+]i) of spermatozoa of the sea urchin Hemicentrotus pulcherrimus. FSG and/or SAP‐I induced elevations of [Ca2+]; and pHi 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 pHi 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 pHi, At pH 6.6, FSG and/or SAP‐I did not induce significant elevation of the [Ca2+]i, although SAP‐I elevated the pHi, 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 pHi 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.