Electron Paramagnetic Resonance Gives Evidence for the Presence of Type 1 Gonadotropin-Releasing Hormone Receptor (GnRH-R) in Subdomains of Lipid Rafts

This study investigated the effect of type 1 gonadotropin releasing hormone receptor (GnRH-R) localization within lipid rafts on the properties of plasma membrane (PM) nanodomain structure. Confocal microscopy revealed colocalization of PM-localized GnRH-R with GM₁-enriched raft-like PM subdomains. Electron paramagnetic resonance spectroscopy (EPR) of a membrane-partitioned spin probe was then used to study PM fluidity of immortalized pituitary gonadotrope cell line αT3-1 and HEK-293 cells stably expressing GnRH-R and compared it with their corresponding controls (αT4 and HEK-293 cells). Computer-assisted interpretation of EPR spectra revealed three modes of spin probe movement reflecting the properties of three types of PM nanodomains. Domains with an intermediate order parameter (domain 2) were the most affected by the presence of the GnRH-Rs, which increased PM ordering (order parameter (S)) and rotational mobility of PM lipids (decreased rotational correlation time (τc)). Depletion of cholesterol by methyl-β-cyclodextrin (methyl-β-CD) inhibited agonist-induced GnRH-R internalization and intracellular Ca²⁺ activity and resulted in an overall reduction in PM order; an observation further supported by molecular dynamics (MD) simulations of model membrane systems. This study provides evidence that GnRH-R PM localization may be related to a subdomain of lipid rafts that has lower PM ordering, suggesting lateral heterogeneity within lipid raft domains.

Effect of flavonoid structure on the fluidity of model lipid membranes

We investigated how the structural properties of (+)-catechin, (-)-epicatechin, (-)-epigallocatechin (EGC) and (-)-epigallocatechin-3-gallate (EGCG) and butylated hydroxytoluene (BHT) correlate with structural changes of phosphatidylcholine plus sphingomyelin (2.4:1) model lipid membranes. Changes were measured by fluorescence anisotropy, electron paramagnetic resonance, and differential scanning calorimetry. Two fluorophores and two spin probes were used to monitor membrane characteristics close to water-lipid interface and in the middle of the bilayer. The data obtained were correlated to the amount of bounded compounds, the number of H-bonds, and the topological polar surface area (TPSA) of the compounds. These correlations reflect the behaviours of (+)-catechin, (-)-epicatechin, EGC, EGCG and BHT. Our results confirm that phenolics studied here are bounded to a membrane surface predominantly via hydrogen bonds, while BTH is inserted into the lipid bilayer.

Single oral inoculation with Escherichia coli (ATCC 25922) stimulates generalised production of nitric oxide in mice

Nitric oxide (NO) production was investigated in the lungs, thoracic aorta, heart, liver, spleen, kidneys and brain of mice inoculated orally with Escherichia coli ATCC 25922. Detection of NO was performed by electron paramagnetic resonance (EPR) using diethyldithiocarbamate (DETC) spin trap. Nitric oxide synthase (NOS) inhibitors [nonselective: L-NAME and inducible NOS (iNOS) selective: 1400W] were used to determine the source of NO. Spin-trap only and untreated mice were included as controls. Within 2.5 hours (h) of a single oral inoculation with E. coli half of the animals had increased NO levels in all investigated organs. Thereafter the signals dropped before increasing again to reach maximal median values by 25 h in all organs of all inoculated mice. The most intense response occurred in livers, followed by aorta and lungs. Early (2.5 h) inhibition of the signal was achieved using both NOS inhibitors. L-NAME was also effective at 25 h, while 1400W-treated mice had increased NO levels beyond 7 h. The generalised increase in NO production in the short and longer term indicates a host response to E. coli administered by the oral route of infection.