The pH within the jelly coat of sea urchin eggs

Because low molecular weight factors isolated from sea urchin egg jelly increase sperm motility and respiration, but only at a pH less than 7.4, H. Ohtake (J. Exp. Zool. 198, 303-312, 1976) suggested that the pH within the jelly experienced by a sperm swimming to the egg might be 6.5-7.0. With a pH microelectrode, the pH in the jelly coat of single eggs of Strongylocentrotus purpuratus and Lytechinus pictus was measured and found to be not significantly different from the pH of seawater, 8.0; it thus does not seem likely that these low molecular weight factors are important in maintaining sperm motility or respiration during fertilization.