Calcium and polyphosphoinositides: their distribution in relation to the membrane changes occurring in the head of boar spermatozoa.
Ejaculated boar spermatozoa, previously incubated in a rigorously Ca++-free medium, were exposed to Ca++ for different incubation times and processed for the detection of Ca++ localization by a pyroantimonate technique. The distribution of polyphosphoinositides, anionic phospholipids natural constituents of membrane known to bind Ca++, was investigated using a specific cytochemical probe, i.e., neomycin conjugated with horseradish peroxidase. The in situ localizations thus obtained revealed: short exposure to Ca++ ions (10 min) evocated a Ca++-induced release of calcium from the nonmitochondrial intracellular store, i.e., the outer acrosomal membrane; a more prolonged exposure (20 min) triggered the occurrence of fusional and exocytotic events, that appeared to be morphologically related to the acrosome reaction; the outer acrosomal membrane, which is the fusigenic sperm membrane, was the elective site of the neomycin/peroxidase labeling. When assayed for the presence of a phospholipase C-like activity, the detergent extract obtained from boar spermatozoa exhibited substantial amount of p-nitrophenyl-phosphorylcholine hydrolyzing activity. The results, on the whole, allow us to suggest a relationship between Ca++ and polyphosphoinositides turnover in the events triggering the acrosome reaction, the exocytotic process peculiar to mammalian spermatozoa.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D006735:Horseradish Peroxidase; D007202:Indicators and Reagents; D008297:Male; D008854:Microscopy, Electron; D009355:Neomycin; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism*; D013094:Spermatozoa / Q000378:metabolism* / Q000648:ultrastructure; D013552:Swine; D010738:Type C Phospholipases / Q000302:isolation & purification
D007202:Indicators and Reagents; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D006735:Horseradish Peroxidase; D010738:Type C Phospholipases; D009355:Neomycin; D002118:Calcium