Lipid changes in rat spermatozoa during isolation and functional activation in vitro

Abstract

Hydrolysis of glycerophospholipids (GPL) and sphingomyelin (SM) are calcium-dependent reactions that are significantly stimulated in rat epididymal spermatozoa during incubations leading to capacitation (Cap) and particularly after acrosomal reaction (AR). In comparison with gametes whose contact during isolation with tissue divalent cations was avoided (C1), or kept to a minimum (C2), those used as controls in these incubations (C3) already had their glycerophospholipids (GPL) and sphingomyelin (SM) partially hydrolyzed. Using C1 as controls, the C3 gametes had less GPL per cell and more free fatty acids. The latter were released with cholesterol from cells to media during albumindependent capacitation. Significant decreases in membrane GPL occurred gradually in the order C1 > C2 > C3 > Cap > AR. Diminution in the major choline GPL specifically targeted phosphatidylcholine in the presence of a virtually unchanged amount of plasmenylcholine, the acrosome-reacted cells thus becoming relatively rich in plasmalogens. The unique SM with very long chain PUFA located on sperm heads was intact in C1 cells and maximally hydrolyzed into ceramides after completion of AR. Using fluorescent probes, liposomes prepared from the 5 conditions showed that C1 gametes had the minimun degree of order of the lipid bilayer, this increasing significantly as Cap andAR proceeded