Increasing intracellular pH of sea urchin sperm with NH4Cl induces Ca2+ uptake and acrosome reaction in the absence of egg jelly

AbstractIntracellular alkalinization and Ca2+ uptake accompany the egg jelly-induced acrosome reaction of sea urchin sperm. Here, sperm were incubated in NF4Cl-containing seawater maintained at its physiological pH (8.0). Under these conditions, 20 mM NH4C1 induced intracellular alkalinization, Ca2+ uptake and acrosome reaction in the absence of egg jelly. The NH4Cl-triggered acrosome reaction required external Ca2+. Our results indicate that internal alkalinization activates Ca2+ influx into sperm possibly through a pH sensitive Ca2+ channel. Thus egg jelly could first stimulate the sperm plasma membrane Na+/H+ exchanger inducing intracellular alkalinization which would then activate Ca2+ uptake and acrosome reactions