An excised patch membrane sensor for arachidonic acid released in mouse hippocampal slices under stimulation of L-glutamate

P450 Eicosanoids and Reactive Oxygen Species Interplay in Brain Injury and Neuroprotection

Significance: Eicosanoids are endogenous lipid mediators that play important roles in brain function and disease. Acute brain injury such as that which occurs in stroke and traumatic brain injury increases the formation of eicosanoids, which, in turn, exacerbate or diminish injury. In chronic neurodegenerative diseases such as Alzheimer's disease and vascular dementia (VD), eicosanoid synthetic and metabolizing enzymes are altered, disrupting the balance between neuroprotective and neurotoxic eicosanoids. Recent Advances: Human and experimental studies have established the opposing roles of hydroxy- and epoxyeicosanoids and their potential utility as diagnostic biomarkers and therapeutic targets in neural injury. Critical Issues: A gap in knowledge remains in understanding the cellular and molecular mechanisms underlying the neurovascular actions of specific eicosanoids, such as specific isomers of epoxyeicosatrienoic (EETs) and hydroxyeicosatetraenoic acids (HETEs). Future Directions: EETs and HETEs exert their actions on brain cells by targeting multiple mechanisms, which include surface G-protein coupled receptors. The identification of high-affinity receptors for EETs and HETEs and their cellular localization in the brain will be a breakthrough in our understanding of these eicosanoids as mediators of cell-cell communications and contributors to brain development, function, and disease. Antioxid. Redox Signal. 28, 987-1007.

Transmembrane Signaling with Lipid-Bilayer Assemblies as a Platform for Channel-Based Biosensing

Artificial and natural lipid membranes that elicit transmembrane signaling is are useful as a platform for channel-based biosensing. In this account we summarize our research on the design of transmembrane signaling associated with lipid bilayer membranes containing nanopore-forming compounds. Channel-forming compounds, such as receptor ion-channels, channel-forming peptides and synthetic channels, are embedded in planar and spherical bilayer lipid membranes to develop highly sensitive and selective biosensing methods for a variety of analytes. The membrane-bound receptor approach is useful for introducing receptor sites on both planar and spherical bilayer lipid membranes. Natural receptors in biomembranes are also used for designing of biosensing methods.

Guanosine and synthetic organoselenium compounds modulate methylmercury-induced oxidative stress in rat brain cortical slices: involvement of oxidative stress and glutamatergic system

Excessive formation of reactive oxygen species (ROS) and disruption of glutamate uptake have been pointed as two key mechanisms in methylmercury-toxicity. Thus, here we investigate the involvement of glutamatergic system in methylmercury (MeHg) neurotoxicity and whether diphenyl diselenide, ebselen and guanosine could protect cortical rat brain slices from MeHg-induced ROS generation. MeHg (100 and 200 microM) increased 2',7'-dichlorodihydrofluorescin (DCFH) oxidation after 2h of exposure. At 50 microM, MeHg increased DCFH oxidation only after 5h of exposure. Guanosine (1 and 5 microM) did not caused any effect per se; however, it blocked the increase in DCFH caused by 200 or 50 microM MeHg. Ebselen (5 and 10 microM) decreased significantly the DCFH oxidation after 2 and 5h of exposure to MeHg. Diphenyl diselenide (5 microM) did not change the basal DCFH oxidation, but abolished the pro-oxidant effect of MeHg. MK-801 also abolished the pro-oxidant effect of MeHg. These results demonstrate for the first time the potential antioxidant properties of organoseleniun compounds and guanosine against MeHg-induced ROS generation after short-term exposure in a simple in vitro model. In conclusion, endogenous purine (guanosine) and two synthetic organoselenium compounds can modulate the pro-oxidant effect of MeHg in cortical brain slices.

Detection of γ-aminobutyric acid-induced glutamate release in acute mouse hippocampal slices with a patch sensor

gamma-Aminobutyric acid (GABA)-stimulated release of L-glutamate from various neuronal regions of acute mouse hippocampal slices was detected with a patch sensor that responds to L-glutamate at the sub-micromolar level. The response of the patch sensor to L-glutamate was evaluated in terms of an integrated current. The integrated current increased with the concentration of L-glutamate ranging from 0.50 to 5.0 microM. By using the patch sensor, GABA-induced L-glutamate release from acute mouse hippocampal slices was detected. The effect of antagonists for GABA(A) and GABA(B) receptors on the L-glutamate release was also investigated. The GABA (25 microM) stimulation induced the release of L-glutamate via GABA(A) receptor in the CA1 region, but GABA did not induce L-glutamate release in the CA3 region. However, in the presence of the GABA(B) receptor antagonist (3-aminopropyl)(diethoxymethyl)phosphinic acid (CGP-35348), release of L-glutamate in the CA3 region was evoked by GABA stimulation. The glutamate release was completely suppressed when both GABA(A) and GABA(B) receptor were inhibited. The current results show that the glutamate release in the CA3 region occurs via a GABA(A) pathway when GABA(B) receptors are inhibited.

Inhibition of ligand binding to G protein-coupled receptors by arachidonic acid

Arachidonic acid (AA), released in response to muscarinic acetylcholine receptor (mAChR) stimulation, previously has been reported to function as a reversible feedback inhibitor of the mAChR. To determine if the effects of AA on binding to the mAChR are subtype specific and whether AA inhibits ligand binding to other G protein-coupled receptors (GPCRs), the effects of AA on ligand binding to the mAChR subtypes (M1, M2, M3, M4, and M5) and to the micro-opioid receptor, beta2-adrenergic receptor (beta2-AR), 5-hydroxytryptamine receptor (5-HTR), and nicotinic receptors were examined. AA was found to inhibit ligand binding to all mAChR subtypes, to the beta2-AR, the 5-HTR, and to the micro-opioid receptor. However, AA does not inhibit ligand binding to the nicotinic receptor, even at high concentrations of AA. Thus, AA inhibits several types of GPCRs, with 50% inhibition occurring at 3-25 MuM, whereas the nicotinic receptor, a non-GPCR, remains unaffected. Further research is needed to determine the mechanism by which AA inhibits GPCR function.