Evidence for tight coupling of phospholipase activation and Ca2+ influx during acrosome reaction of golden hamster spermatozoa.
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. Upon exposure of the spermatozoa to 1.7 mM Ca2+, a net uptake by the cells occurred in two distinguishable phases. 3. Depletion of extracellular Ca2+ by ethylene glycol bis(beta-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. The time course of an initial Ca2+ uptake seemed to precede that of the acrosome reaction. 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. Phospholipase A2 activation, detected by lysophospholipid formation, slightly delayed the initial events of first Ca2+ uptake and phosphatidic acid production. 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.
Imai
A
A
Department of Obstetrics and Gynecoloy, Gifu University School of Medicine, Japan.
Iida
K
K
Matsunami
K
K
Matsuda
T
T
Tamaya
T
T
D000177:Acrosome / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006224:Cricetinae; D004789:Enzyme Activation; D005990:Glycerol / Q000378:metabolism; D008297:Male; D008647:Mesocricetus; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010740:Phospholipases / Q000502:physiology*; D013081:Sperm Motility / Q000502:physiology; D013094:Spermatozoa / Q000378:metabolism*
D010714:Phosphatidylethanolamines; D010740:Phospholipases; D005990:Glycerol; D002118:Calcium