Incorporating Lipids into Boar Sperm Decreases Chilling Sensitivity but Not

Fresh boar sperm were incubated with small unilamellar li-posomes composed of either the total lipids extracted from head plasma membranes (HPM) of fresh boar sperm or selected lipids (SL) of five defined phospholipids with specific acyl chains. To optimize fusion, liposomes with 2 mol % octadecyl rhodamine fluorophore in Beltsville Thawing Solution 6 1 mM CaCl2 were incubated at 358C with 1 3 107 or 108 spermatozoa/ml and monitored over 60 min, using flow cytometry and fluorescence microscopy. The HPM fused to both sperm concentrations faster than SL but was equivalent by 30 min (108 sperm/ml) or 60 min (107 sperm/ml; 57.5 6 3 % and 67.1 6 8 % sperm fused to HPM and SL, respectively) 6 Ca21. Neither HPM nor SL affected onset of capacitation or spontaneous or ionophore-induced acrosome reactions at 0 or 3 h (chlortetracycline and fluorescein isothio-cyanate-Pisum sativum agglutinin; n 5 3). During cooling and after cryopreservation (n 5 4 ejaculates), SL but not HPM sig-nificantly improved sperm motility and viability (Sybr14/propi-dium iodide staining) 6 20 % egg yolk, but egg yolk alone was more effective than SL alone. Liposomes of complex composi-tion can fuse to boar sperm without harming in vitro capacita-tion or acrosome reaction and reduce sperm chilling sensitivity. sperm, sperm capacitation/acrosome reactio