Lipid biochemical-biophysical correlations during isolation and functional activation of rat spermatozoa

PEÑALVA, D.A.; ORESTI, G.M.; LUQUEZ, J.M.; ANTOLLINI, S.S.; AVELDAÑO, M.I.

Conferencia; 56th Meeting of the International Conference on the Bioscience of Lipids (ICBL); 2015

The aim of this study was to evaluate how hydrolytic changes occurringin rat sperm lipids after isolation and after incubations that promotecapacitation (Cap) or the acrosomal reaction (AR) affect the sperm membranebiophysical state, evaluated from changes in Laurdan fluorescencegeneralized polarization values (GPv). In gametes isolated in the presence of adivalent cation chelator, no lipid changes occurred and GPv were the lowest,indicative of maximal membrane lipid mobility. However rapid and gentle,isolation in the absence of chelators led to part of the sphingomyelins (SM)being converted into ceramides (Cer), significantly increasing GPv. When thesesamples were incubated as controls for Cap and AR, unchanged cholesterol levelsconcurred with the highest accumulation of free fatty acids (FFA), resulting ineven higher GPv. After completion of Cap, the GPv droped down again, whichcoincided with spermatozoa having lost part of their cholesterol to the mediumand most of their FFA during the incubation; in addition, their PUFA-containingplasmalogen levels had decreased less than did the phosphatidylglycerophospholipid subclasses. The highest GPv coincided with the highestCer/SM ratio, both occurring in Cap samples after completion of AR.Interestingly, a degree of SM?¨Cer conversion, which correlated with the extentof AR, spontaneous or induced, occurred in the background in all samples,including controls. Cholesterol, FFA and Cer, independently and additively,augmented GPv when added to liposomes prepared from the polar lipid of intactsperm. Hydrolytic changes that affect rat sperm lipids, not only afterincubations but also after usual laboratory manipulations during isolation,result in significant changes in the membrane biophysical state.