Involvement of Wheat Germ Agglutinin (WGA)-Binding Protein in the Induction of the Acrosome Reaction of the Sea Urchin, Strongylocentrotus intermedius. II. Antibody against WGA-Binding Protein Induces the Acrosome Reaction: WGA-binding protein/sea urchin/sperm/acrosome reaction

TLDR: The results suggest that the WGAbp on the sperm plasma membrane is involved in the regulation of Ca2+ influx and Na+/H+ exchange associated with the AR of S. intermedius sperm, a strong candidate for the receptor of the AR‐inducing substance in the egg jelly.

Abstract: We obtained a polyclonal antibody against the WGA-binding protein (WGAbp) of Strongylocentrotus intermedius sperm, which is a membrane glycoprotein of 260 kD under non-reducing condition Anti-WGAbp antibody induced increases in both intracellular Ca2+ ([Ca2+]i) and intracellular pH (pHi), resulting in the onset of the AR The increases in [Ca2+]i and pHi required extracellular Ca2+ and Na+, respectively, and were suppressed by the pretreatment with WGA, resulting in the inhibition of the AR Anti-WGAbp antibody-induced AR was inhibited also by lowered extracellular pH elevated K+, removal of Na+ from seawater and the treatment with verapamil, a Ca2+ channel inhibitor These inhibitory conditions are identical with those of the egg jelly-induced AR Monovalent Fab fragments from anti-WGAbp antibody also induced the AR at relatively high concentration These results suggest that the WGAbp on the sperm plasma membrane is involved in the regulation of Ca2+ influx and Na+/H+ exchange associated with the AR of S intermedius sperm It is a strong candidate for the receptor of the AR-inducing substance in the egg jelly