Efficient photoanode with a MoS2/TiO2/Au nanoparticle heterostructure for ultraviolet-visible photoelectrocatalysis.

Green energy technology is generally becoming one of hot issues that need to be solved due to the adverse effects on the environment of fossil fuels. One of the strategies being studied and developed by theorists and experimentalists is the use of photoelectrochemical (PEC) cells, which are emerging as a candidate to produce hydrogen from water splitting. However, creating photoelectrodes that meet the requirements for PEC water splitting has emerged as the primary obstacle in bringing this technology to commercial fruition. Here, we construct a heterostructure, which consists of MoS2/TiO2/Au nanoparticles (NPs) to overcome the drawbacks of the photoanode. Owing to the dependence on charge transfer, the bandgap of MoS2/TiO2and the utilization the Au NPs as a stimulant for charges separation of TiO2by localized surface plasmon resonances effect as well as the increase of hot electron injection to cathode, leading to photocatalytic activities are improved. The results have recorded a significant increase in the photocurrent density from 2.3µAcm-2of TiO2to approximately 16.3µAcm-2of MoS2/TiO2/Au NPs. This work unveils a promising route to enhance the visible light adsorption and charge transfer in photo-electrode of the PEC cells by combining two-dimensional materials with metal NPs.

Isolation of Gram-positive Firmibacteria as major eicosapentaenoic acid producers from subtropical marine sediments.

In this study, a total of 172 putative omega-3 producers were isolated from 28 sediment samples from the Arabian Gulf employing a selective isolation procedure using marine agar containing 0·1% triphenyl tetrazolium chloride (TTC). Out of these 172 isolates, 19 isolates produced eicosapentaenoic acid (EPA) as confirmed by Gas Chromatography-Mass Spectrometry (GC-MS). The EPA content of the isolated bacterial strain varied from 1·76 to 6·52% of total fatty acids. Among the 19 isolates of EPA producers, while 17 isolates harboured both pfaA gene and Δ6 desaturase gene, only five isolates harboured Δ5 desaturase gene. Two of the EPA positive strains harbour none of the three genes tested. The 16s RNA identification of these isolates revealed that except one, all the EPA producers were Gram-positive marine bacteria belonging to the phylum Firmicutes, family Bacillacea, genera Bacillus and Oceanobacillus. Halomonas pacifica was the only Gram-negative Gamma-Proteobacteria detected to produce EPA from this region. SIGNIFICANCE AND IMPACT OF THE STUDY: Recently, marine bacteria are considered as a promising source of polyunsaturated fatty acid (PUFA) over marine fishes and microalgae. PUFA producers reported from polar and deep-sea sources were restricted to five well-known marine genera under two distinct domains of bacteria such as proteobacteria (Shewanella, Colwellia, and Moritella) and cytophaga group (Flexibacter, Psychroflexus). This study revealed that subtropical marine environment could also be the source of PUFA producing bacteria, and they predominantly belonged to the class of Firmibacteria. This finding opens up new avenue for research to study the inherent mechanism and physiology of such organisms from this unique environment.

Arachidonic acid induces ERK activation via Src SH2 domain association with the epidermal growth factor receptor.

Within the kidney, angiotensin II type 2 (AT(2)) receptor mediates phospholipase A(2) (PLA(2)) activation, arachidonic acid release, epidermal growth factor (EGF) receptor transactivation, and mitogen-activated protein kinase activation. Arachidonic acid mimics this transactivation by an undetermined mechanism. The role of c-Src in mediating angiotensin II and arachidonic acid signaling was determined by employing immunocomplex kinase assay, Western blotting analysis, and protein immunoblotting on co-precipitated EGF receptor (EGFR) proteins and agarose conjugates of glutathione S-transferase fusion proteins containing the c-Src homology 2 (SH2) and SH3 domains. Angiotensin II induced extracellular signal-regulated kinase (ERK) activation in primary cultures of rabbit proximal tubule cells via the activation of c-Src and association of the EGFR with the c-Src SH2 domain, effects that were mimicked by arachidonic acid and its inactive analogue eicosatetraynoic acid. Inhibition of PLA(2) by mepacrine and methyl arachidonyl fluorophosphate, AT(2) receptor by PD123319, Src family kinases by, 1-(tert-butyl)-3-(4-chlorophenyl)-4-aminopyrazolo[3,4-d] pyrimidine (PP2) and c-Src by overexpression of a dominant-negative mutant of c-Src abrogated these effects. However, inhibitors of arachidonic acid metabolic pathways did not block these effects. The present work provides a new and novel paradigm for transactivation of a kinase receptor linked to a fatty acid, which may apply to activation of a variety of phospholipases and accompanying arachidonic acid release.

Coordinate regulation of metabotropic glutamate receptors.

Recent studies aimed at identifying the mechanisms that regulate the signaling of metabotropic glutamate receptors (mGluRs) have revealed that both protein kinase and protein phosphatase activity are important in directly modulating mGluR function. The inter-relationship between phosphorylation and dephosphorylation of mGluRs seems to be an important determinant in regulating mGluR function and the subsequent neuromodulatory events elicited by activation of mGluRs.

Activation of NMDA receptors reverses desensitization of mGluR5 in native and recombinant systems.

The metabotropic glutamate receptor, mGluR5, has a critical role in induction of NMDA-receptor-dependent forms of synaptic plasticity and excitotoxicity. This is likely mediated by a reciprocal positive-feedback interaction between these two glutamate receptor subtypes in which activation of mGluR5 potentiates NMDA receptor currents and NMDA receptor activation potentiates mGluR5-mediated responses. We have investigated the mechanism by which NMDA receptor activation modulates mGluR5 function and find evidence that this response is mediated by activation of a protein phosphatase and a resultant dephosphorylation of protein kinase C phosphorylation sites on mGluR5. This form of neuromodulation may be important in a number of normal and pathological processes that involve activation of the NMDA receptor.

Effects of moderate, central fluid percussion traumatic brain injury on nitric oxide synthase activity in rats.

Experimental traumatic brain injury (TBI) damages cerebral vascular endothelium and reduces cerebral blood flow (CBF). The nitric oxide synthase (NOS) substrate, L-arginine, prevents CBF reductions after TBI, but the mechanism is not known. This study examined the possibility that post-traumatic hypoperfusion is due to reductions in the substrate sensitivity of NOS which are overcome by L-arginine. Isoflurane-anesthetized rats were prepared for TBI (midline fluid-percussion, 2.2 atm), sham-TBI, or no surgery (control), and were decapitated 30 min after injury or sham injury. The brains were removed and homogenized or minced for measurements of crude soluble or cell-dependent stimulated NOS activity, respectively. Baseline arterial oxygen, carbon dioxide, pH, or hemoglobin levels did not differ among control, sham, or TBI groups. Total cortical soluble NOS activity in TBI-treated rats was not significantly different from either untreated or sham groups when 0.45 microM or 1.5 microM L-arginine was added. Also, there were no differences in cell-dependent NOS activity among the three groups stimulated by 300 microM N-methyl-D-aspartate, 50 mM K+, or 10 microM ionomycin. These data suggest that TBI reduces CBF by a mechanism other than altering the substrate specificity or activation of nNOS.

HIV decreases glutamate transport in SK-N-MC neuroblastoma cells.

Autopsy studies of patients with AIDS dementia have shown neuronal loss consistent with a neurotoxic component of this disease. In vitro studies suggest that viral products or cytokines from HIV-infected macrophages (Mphi) may modulate or directly mediate excitotoxic cell death of neurons. Mphi differentiated from peripheral mononuclear blood cultures were infected with HIV, and conditioned media (CM) were harvested from these cultures. Exposure of SK-N-MC (neuroblastoma) cells to CM from HIV-infected Mphi for 4, 24 or > or = 48 h resulted in a mean suppression of 12-34% of the glutamate transport Vmax with no appreciable change in transport Km. An astrocytoma tumor cell, U373MG, showed similar CM-mediated glutamate uptake suppression. Changes were evident in total and Na+-dependent glutamate uptake, with significantly more suppression of Na+-dependent uptake. Similar effects were seen with the nonmetabolizable transporter agonist D-aspartate, indicating that the effect was on transport and not metabolism. No suppression was seen with CM from uninfected Mphi or Mphi infected with heat-inactivated HIV. The magnitude of uptake suppression was not correlated with CM p24 values, and removal of CM virions by ultracentrifugation and immunoprecipitation did not alter the uptake-suppressive properties of infected Mphi CM. Uptake suppression was seen when Mphi were infected with Mphi-tropic strains HIV(SF162), HIV(JR-CSF), HIV(NFN-SX) and a Mphi-tropic patient isolate, but not the lymphotropic strain HIV(LAI). HIV-infected Mphi may produce substances which suppress neuronal and glial glutamate neurotransmitter uptake, resulting in higher extracellular glutamate levels and leading possibly to deficits in cell signaling and neurotoxicity.

Dopamine neurotoxicity in cortical neurons.

Dopamine (DA), at concentrations greater than 100 microM, has previously been demonstrated to be toxic to mesencephalic, striatal and dorsal root ganglion cell cultures. Pharmacological experiments suggest that DA also may play a role in the cortical neurotoxicity caused by systemic administration of N-methyl-D-aspartate receptor antagonists such as phencyclidine and MK-801. In this study, the potential toxicity of DA in primary cortical cell cultures was determined in vitro. Using calcein and ethidium homodimer fluorescence as a marker for live and dead cells, respectively, we observed that a 24 h treatment with 10-100 microM DA produced a concentration-dependent increase in the number of ethidium homodimer-labelled cells. The cell death induced by 10 microM DA was dramatically reduced by co-administration of either superoxide dismutase and catalase or deferoxamine mesylate, an iron chelator. To verify this observation, the effects of 10 microM DA on the release of cytoplasmic lactate dehydrogenase (LDH) was measured. DA increased LDH release in a manner that was inhibited by both superoxide dismutase/catalase and deferoxamine. Nomifensine potentiated the effect of DA on LDH release, suggesting a protective role for DA uptake in this system. On the other hand, neither D1 nor D2 antagonists were able to prevent DA-induced LDH release. These data suggest that relatively low concentrations of DA can be injurious to cortical neurons through a mechanism that likely involves DA autooxidation and the formation of reactive oxygen species such as superoxide anion and hydroxyl radical. This mechanism may be important in the toxic effects of psychomotor stimulants such as amphetamine. However, the failure of DA receptor antagonists to affect DA-induced injury argues that the effect of DA on cortical neurons in culture does not model the toxic effect of phencyclidine and MK-801 observed in vivo.

Voltage-dependent calcium channel involvement in NMDA-induced activation of NOS.

We have previously shown that N-methyl-D-aspartate (NMDA) increases nitric oxide synthase (NOS) activity in rat frontal cortex; however, the actual mechanism of this activation has not been addressed. Tetrodotoxin (TTX; 0.05 microM) inhibited NMDA-activated NOS, suggesting that TTX-sensitive Na+ channels are interposed between the NMDA receptors and the NOS cellular compartment. The NMDA response was also blocked by voltage-dependent Ca2+ channel (VDCC) blockers including Cd2+, Co2+, funnel web spider toxin (FTX) and omega-Aga IVa, but not by nifedipine or omega-conotoxin. These data suggest that Ca2+ flux through P- and/or Q-type VDCC subsequent to NMDA-induced depolarization may be at least as important for NOS activation as Ca2+ entry through the NMDA receptor.

Regulation of nitric oxide synthase activity in cortical slices by excitatory amino acids and calcium.

Nitric oxide synthase (NOS) activity was determined in adult rat frontal cortex and hippocampus by measuring the conversion of L-[3H]arginine to L-[3H]citrulline. N-methyl-D-aspartate (NMDA), but not kainate or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), stimulated NOS activity. This effect was concentration dependent (EC50 approximately 30 microM) and was inhibited by tetrodotoxin, EGTA, N omega-nitro-L-arginine (NOARG), Mg2+, phencyclidine, and (cis)-4-phosphonomethyl-2-piperidine carboxylate (CGS 19755), but not by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). NOS activity was increased to an even greater extent by the calcium ionophores ionomycin and A23187 and by depolarization with 50 mM K+. Interestingly, neither caffeine nor 1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD), drugs that would be expected to increase intracellular Ca2+ concentration by release of Ca2+ from intracellular ryanodine- and inositol-1,4,5-trisphosphate-sensitive stores, respectively, had any significant effect on NOS activity. It is concluded that NOS can be activated by NMDA binding to a classic NMDA glutamate receptor subtype as well as by depolarization or other agents that increase the influx of extracellular Ca2+. The paradoxical lack of effect of caffeine, as well as the inhibitory effect of tetrodotoxin, are discussed.

The role of P-type calcium channels in the depolarization-induced activation of nitric oxide synthase in frontal cortex.

In this study we demonstrate that 50 mM K+ stimulates the conversion of L-[3H]arginine to L-[3H]citrulline and that this effect is blocked by 10 microM N omega-nitro-L-arginine, a nitric oxide synthase inhibitor, and Ca(2+)-free conditions. Amiloride (1 mM) and low Na+ conditions were used to test the possible involvement of the Na(+)-Ca2+ exchanger. These treatments were without effect. The calcium channel blockers 10 mM Mg2+, 100 microM Cd2+, and 10 mM Co2+ also blocked the K+ response, suggesting the involvement of voltage-dependent calcium channels (VDCCs). The specific VDCC involved seems to be the P type, as funnel-web spider toxin blocked the response whereas 200 microM Ni2+, 10 microM nifedipine, and 100 nM omega-conotoxin did not.

(R,S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors mediate a calcium-dependent inhibition of the metabotropic glutamate receptor-stimulated formation of inositol 1,4,5-trisphosphate.

L-glutamate (3-1,000 microM) and (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD; 10-1,000 microM), a selective agonist for the metabotropic glutamate receptor, stimulated the formation of inositol 1,4,5-trisphosphate in a concentration-dependent manner. L-Glutamate was half as efficacious as 1S,3R-ACPD. N-methyl-D-aspartate (NMDA; 1 nM to 1 mM) did not significantly influence the response to a maximally effective concentration of 1S,3R-ACPD (100 microM). On the other hand, coapplication of (R,S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA; 1-300 nM) produced a concentration- and time-dependent inhibition of the 1S,3R-ACPD effect, with a maximal inhibition (97%) at 100 nM. Ten micromolar 6-cyano-7-nitroquinoxaline-2,3-dione, an antagonist of the AMPA receptor, blocked the inhibitory effect of AMPA. Reduced extracellular calcium concentration, as well as 10 microM nimodipine, an L-type calcium channel antagonist, inhibited the AMPA influence on the 1S,3R-ACPD response. W-7, a calcium/calmodulin antagonist, prevented the inhibition by AMPA, whereas H-7, an inhibitor of protein kinase C, had no effect. These data suggest that activation of AMPA receptors has an inhibitory influence on inositol 1,4,5-trisphosphate formation mediated by stimulation of the metabotropic glutamate receptor. The mechanism of action involves calcium influx through L-type type calcium channels and possible activation of calcium/calmodulin-dependent enzymes.

Inhibition of the phospholipase C-linked metabotropic glutamate receptor by 2-amino-3-phosphonopropionate is dependent on extracellular calcium.

D,L-2-Amino-3-phosphonopropionate (AP-3), a proposed metabotropic receptor antagonist, produced a concentration-dependent increase in the formation of inositol 1,4,5-trisphosphate in rat hippocampal slices. The response was maximal at 1 mM and completely due to the L-isomer. D,L-AP-3 was half as efficacious as (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD), a selective agonist of this receptor. The response produced by maximally effective concentrations of L-AP-3 and 1S,3R-ACPD together for 5 min was not significantly different from that produced by 1S,3R-ACPD alone. However, pretreatment for 40 min with either 1 mM L-AP-3 or D,L-AP-3 completely inhibited the response to 1S,3R-ACPD. This inhibition was long-lasting (wash-resistant) and was reversed by reduction of the extracellular Ca2+ concentration. Also, pretreatment for 40 min with 1S,3R-ACPD reduced, but did not completely block, the response to readdition of 1S,3R-ACPD. L-AP-3 (1 mM) also produced a stereoselective 2.3-fold increase in the efflux of glutamate from the hippocampal slices. These data suggest that incubation of hippocampal slices with AP-3 induces a time-dependent desensitization of the metabotropic response by a mechanism that is dependent on extracellular Ca2+. The possible roles of receptor occupancy and inhibition of glutamate uptake by AP-3 are also discussed.

Localization of the P3 sources using magnetoencephalography and magnetic resonance imaging.

In this study, two related issues were addressed: first, whether the P3 component of auditory evoked responses, obtained in the context of an oddball paradigm, and its magnetoencephalographically recorded counterpart (P3m) are generated by the same intracranial sources; and, second, whether these sources, modeled as equivalent current dipoles, can be localized in particular brain structures using magnetic resonance imaging. The study involving 8 normal adult subjects resulted in the following findings. (1) Both the similarities and differences in wave form characteristics of the simultaneously recorded P3 and P3m can be best accounted for by common intracranial sources. (2) Several successively activated single-dipolar sources, rather than a single source, account for the entire evolution of the P3m component. (3) Most of these sources were localized in the vicinity of the auditory cortex in all subjects, although some sources appeared to be in deeper structures, possibly the lateral thalamus. (4) The successive activation of sources followed an orderly medial-to-lateral course. These results suggest that activity responsible for the surface-recorded P3 (and P3m) component may be initiated in deep structures, but it quickly spreads over and is sustained in areas near the auditory cortex.