"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.

Iguazú

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

The aim of this study was to evaluate how hydrolytic changes occurring in rat sperm lipids after isolation and after incubations that promote capacitation (Cap) or the acrosomal reaction (AR) affect the sperm membrane biophysical state, evaluated from changes in Laurdan fluorescence generalized polarization values (GPv). In gametes isolated in the presence of a divalent 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 these samples were incubated as controls for Cap and AR, unchanged cholesterol levels concurred with the highest accumulation of free fatty acids (FFA), resulting in even higher GPv. After completion of Cap, the GPv droped down again, which coincided with spermatozoa having lost part of their cholesterol to the medium and most of their FFA during the incubation; in addition, their PUFA-containing plasmalogen levels had decreased less than did the phosphatidyl glycerophospholipid subclasses. The highest GPv coincided with the highest Cer/SM ratio, both occurring in Cap samples after completion of AR. Interestingly, a degree of SM→Cer conversion, which correlated with the extent of 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 intact sperm. Hydrolytic changes that affect rat sperm lipids, not only after incubations but also after usual laboratory manipulations during isolation, result in significant changes in the membrane biophysical state.