ABSTRACT
It is known that sea urchin sperm undergo spontaneous acrosome reaction (AR) in high pH sea water. It remains unclear why and how AR occurs. Since the increases in intracellular Ca2+ ([Ca2 +]i) and pH (pHi) are necessary for the induction of the AR by egg jelly, we examined the relations of external pH (pHe) to [Ca2+]i and pHi of Hemicentrotus pulcherrimus sperm.
