Bicarbonate/CO₂ induces rapid activation of phospholipase A₂ and renders boar spermatozoa capable of undergoing acrosomal exocytosis in response to progesterone

Abstract

We tested whether capacitation, a phenomenon that renders spermatozoa capable of undergoing acrosomal exocytosis, may be completed rapidly after a short exposure to bicarbonatelCO2. We found that, in the presence of Ca 2+, a 10-min exposure of boar spermatozoa to bicarbonate led to a partial activation of phospholipase A2, primed spermatozoa for a major subsequent activation of this enzyme upon stimulation with progesterone and furthermore rendered spermatozoa capable of undergoing exocytosis in response to this steroid. These results suggest that capacitation may be completed in a relatively short period of time and open up new possibilities for unravelling molecular mechanisms underlying this process.

Very Long-chain Polyunsaturated Fatty Acids Are the Major Acyl Groups of Sphingomyelins and Ceramides in the Head of Mammalian Spermatozoa

“…The proposed endogenous, SMase-catalyzed generation of Cer from SM could be of equal physiological importance to the production of free fatty acids, lysophospholipids, and diacylglycerols by activation of plasma membrane phospholipases, including phospholipase C (38) and phospholipase A 2 (39). In all three cases lipid catabolytes are produced that are potential destabilizers of the sperm membrane when generated in situ, increasing its fluidity and instability and promoting fusion events.…”

Incorporating Lipids into Boar Sperm Decreases Chilling Sensitivity but Not Capacitation Potential1

“…The involvement of the polyphosphatidyl inositol pathway in capacitation and the AR [75][76][77] clearly implicates membrane phospholipids directly in the AR. The postcryopreservation loss of SPH and increase in 20:4 in boar sperm head membranes may indicate early or abnormal ARs, because induced AR in epididymal sperm reduce SPH [72] and 20:4 can initiate an AR either directly [78] or via the polyphosphoinositide cycle as seen in fragile aged sperm [79]. Because neither SL nor HPM liposomes altered the induction of capacitation or the AR, a decrease in the membrane protein:lipid ratio to the extent induced by this fusion must be insufficient to affect these events.…”

Roles of Intracellular Cyclic AMP Signal Transduction in the Capacitation and Subsequent Hyperactivation of Mouse and Boar Spermatozoa

“…The details of capacitation-associated changes in mouse spermatozoa have already been reviewed in well-known publications [e.g ., 4, 28, 29]. For boar spermatozoa, there are reports available on the phospholipid changes in the plasma membrane [30, 31]; aggregation of lipid ordered microdomains (lipid rafts), probably in response to the depletion of cholesterol from the plasma membrane [32, 33]; organization of the docking SNARE complex (VAMP 3, syntaxin 1B and SNAP 23) leading to the stable docking between the plasma membrane and outer acrosomal membrane [34], followed by disassembly of this docking complex and assembly of the fusion-driving SNARE complex (syntaxin 3, SNAP 23 and VAMP 2) with an additional interacting protein (complexin 2) [35]; changes in surface glycoconjugates [36]; increases and decrease in phosphorylated proteins [37, 38]; increases in intracellular calcium [39,40,41]; activation of phospholipase A2 [42]; and changes in the expression and localization of actin [43, 44]. These capacitation-associated changes enable the spermatozoa to undergo their acrosome reaction in the heads and hyperactivation in their flagella.…”