STUDY OF FACTORS INVOLVED IN INDUCTION OF ACROSOMAL REACTION IN SPERM OF SEA-URCHIN, ARBACIA-PUNCTULATA

Several factors involved in induction of the acrosomal reaction in sperm of the sea urchin A. punctulata, were investigated quantitatively using a simple substrate film technique to monitor extension of the acrosomal process by EM. Verification of typical acrosomal process formation was accomplished using thin secretions. Sperm underwent the acrosomal reaction in artificial sea water in the absence of egg jelly coat at pH values > 9.6. In the presence of egg jelly a high percentage of sperm reacted at pH 8.6. At this pH the fraction of sperm that underwent the acrosomal reaction was directly proportional to the concentration of egg jelly. The Ca2+ ionophore A23187 induced the acrosomal reaction in the absence of egg jelly at pH 8.6. The proportion of sperm that reacted was dependent on the concentration of ionophore and on the concentration of Ca2+ in the medium. Pretreatment of sperm with low levels of La3+ which is known to be a Ca2+ ion antagonist, resulted in inhibition of egg jelly induction of the acrosomal reaction. There seemed to be marked similarities between the acrosomal reaction in sea urchin sperm and membrane fusion dependent secretory processes in other cell types.