Lipid Biochemical and Biophysical Changes in Rat Spermatozoa During Isolation and Functional Activation In Vitro

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

BIOLOGY OF REPRODUCTION

SOC STUDY REPRODUCTION

Lugar: Madison; Año: 2015 vol. 140 p. 1 - 13

0006-3363

In spermatozoa isolated from rat epididymis, lipids are differentially modified after in vitro induction of capacitation (Cap) and the acrosomal reaction (AR). In this study, the effects of lipid changes occurring after isolation and after these functional reactions on sperm membrane biophysical alterations were 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. In sperm isolated as rapidly and gently as possible in the absence of chelator, part of the sphingomyelins (SM) were converted into ceramides (Cer), increasing GPv. In samples incubated as controls for Cap and AR, unchanged cholesterol and reduced glycerophospholipid (GPL) levels concurred with accumulation of free fatty acids (FFA), further increasing GPv. After completion of Cap the increased GPv were reduced, as spermatozoa lost part of their cholesterol and FFA. Cap samples became relatively enriched in PUFA-containing plasmalogens, as hydrolysis affected phosphatidyl rather than plasmenyl GPL subclasses. The highest Cer/SM ratio, and the highest GPv, resulted after completion of AR, as induced by A23187. The degree of SM→Cer conversion among samples, including controls, correlated with the extent of AR. FFA and Cer augmented GPv when added to liposomes prepared from the membrane lipid of intact sperm. Our results underscore the importance of hydrolytic changes that affect sperm lipids, especially the decisive lipid SM/Cer pair, not only after inducing sperm functional changes like Cap and AR, but also in control conditions.