Laurdan fluorescence spectroscopy reveals a single liquid-crystalline lipid phase and lack of thermotropic phase transitions in the plasma membrane of living human sperm

Abstract

Membrane lipid phase(s), phase coexistence, and thermotropic phase transitions have been investigated in viable human spermatozoa using Laurdan fluorescence spectroscopy. Generalized polarization (GP) values derived from Laurdan excitation and emission spectra confirm that the sperm plasma membrane is a low polar, highly rigid (liquid-ordered) structure, and give evidence that, in the range from 10 degrees C to 42 degrees C, membrane lipids are in a single liquid-crystalline phase. The absence of phase transitions in the same thermal range argues against the hypothesis that the lipid domains previously detected on the sperm surface are produced by lipid lateral phase separation. The above findings are likely accounted for by the high cholesterol to phospholipid molar ratio found in the human sperm membrane. This is the first time that membrane lipid phase and polarity have been detected and quantified in living mammalian spermatozoa.

Microenvironmental pH Is a Key Factor for Exosome Traffic in Tumor Cells

“…Membrane Fluidity Assay-To analyze membrane fluidity, the exosomes released from cells cultured at acidic or buffered pH values and parental cells were loaded with the fluorescent probe Laurdan (20) as previously described (21). Briefly, Laurdan from a DMSO stock solution (Laurdan and DMSO final concentrations of 0.11 M and 0.06%, respectively) was added to Mel1 cells (1 ϫ 10 6 ) or exoMel1 (50 g) resuspended in 2.5 ml of MES buffer, and the probe loading was allowed to proceed in the dark at 37°C for 45 min.…”

Semen cryopreservation in Bactrian camel (Camelus bactrianus) using SHOTOR diluent: Effects of cooling rates and glycerol concentrations

“…Membranes that have lipids with unsaturated fatty acids or short carbon chains are more fluid at low temperatures [26,27]; therefore, they are more chilling resistant. In species like human, with unusual high sterol content, an abrupt liquid phase transition does not occur; therefore, their sperm are quite resistant to the cold shock [28][29][30]. However, in species like the pig, elephant and horse that require immediate liquid phase transition, fast cooling might be detrimental to sperm cells [22,30,31].…”

Thermo-sensitive response based on the membrane fluidity adaptation inParamecium multimicronucleatum

“…Laurdan in the lipid phase shows spectral sensitivity with a red shift of the emission maximum when passing from a gel to a liquid crystalline phase (Chong and Wong, 1993;Parasassi et al, 1990;Parasassi et al, 1991;Sheffield et al, 1995). Based on this property, laurdan has been used to estimate the fluidity of the membrane in various living cells (Chapman et al, 1995;Harris et al, 2001;Mamdouh et al, 1998;Palleschi and Silvestroni, 1996;Sasaki et al, 2006;Vest et al, 2004;Yu et al, 1996).…”