EVIDENCE FOR TIGHT COUPLING OF PHOSPHOLIPASE ACTIVATION AND CA-2+ INFLUX DURING ACROSOME REACTION OF GOLDEN-HAMSTER SPERMATOZOA

1. 1. Phospholipases have been proposed to play a key role in sperm acrosome reaction. To examine the activation mechanism of phospholipases and subsequently sperm fertilizing capacity, Ca2+ fluxes and phospholipid turnover (breakdown and synthesis) were investigated in golden hamster spermatozoa during acrosome reaction. 2. 2. Upon exposure of the spermatozoa to 1.7 mM Ca2+, a net uptake by the cells occurred in two distinguishable phases. 3. 3. Depletion of extracellular Ca2+ by ethylene glycol bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) at a time that an initial Ca2+ uptake was observed to reach almost steady-state, prevented the secondary Ca2+ uptake and acrosome reaction. 4. 4. The time course of an initial Ca2+ uptake seemed to precede that of the acrosome reaction. 5. 5. Incubation of the spermatozoa with Ca2+ in the presence of [3H]glycerol induced a rapid increase in labeling of phosphatidic acid, a key intermediate of phosphinositide turnover initiated by the action of phospholipase C, which appeared to parallel the time course of a first phase of Ca2+. 6. 6. Phospholipase A2 activation, detected by lysophospholipid formation, slightly delayed the initial events of first Ca2+ uptake and phosphatidic acid production. 7. 7. It is concluded that first Ca2+ entry into the cells, associated with phosphatidic acid production, activates a phospholipase A2, leading to the production of substances, like lysophospholipids and fatty acids, which may contribute to acrosome reaction. © 1990.