Histamine has been shown to play a role in arthropod vision; it is the major neurotransmitter of arthropod photoreceptors. Histamine-gated chloride channels have been identified in insect optic lobes. We report the first isolation of cDNA clones encoding histamine-gated chloride channel subunits from the fruit fly Drosophila melanogaster. The encoded proteins, HisCl1 and HisCl2, share 60% amino acid identity with each other. The closest structural homologue is the human glycine ␣3 receptor, which shares 45 and 43% amino acid identity respectively. Northern hybridization analysis suggested that hisCl1 and hisCl2 mRNAs are predominantly expressed in the insect eye. Oocytes injected with in vitro transcribed RNA, encoding either HisCl1 or HisCl2, produced substantial chloride currents in response to histamine but not in response to GABA, glycine, and glutamate. The histamine sensitivity was similar to that observed in insect laminar neurons. Histamine-activated currents were not blocked by picrotoxinin, fipronil, strychnine, or the H2 antagonist cimetidine. Co-injection of both hisCl1 and hisCl2 RNAs resulted in expression of a histamine-gated chloride channel with increased sensitivity to histamine, demonstrating coassembly of the subunits. The insecticide ivermectin reversibly activated homomeric HisCl1 channels and, more potently, HisCl1 and HisCl2 heteromeric channels.Histamine has been recognized for several years as the major neurotransmitter of arthropod photoreceptors (1, 2). In Drosophila, immunocytochemistry has shown high levels of histamine in photoreceptors and their synapses (2, 3). Further, histidine decarboxylase activity has been demonstrated in Drosophila photoreceptors, suggesting that histamine is synthesized in these cells (2). Drosophila mutants that are deficient in the hdc gene coding for histamine decarboxylase have been identified (4), and flies homozygous for the null mutation appear to be blind (5). Although light-dependent release of histamine from photoreceptors has not yet been demonstrated, exposure of the fly postsynaptic neuron to histamine mimics the effects of light (6).Phototransduction of invertebrates has been most extensively studied in insects, but histamine has been implicated as a neurotransmitter in photoreceptors of several other invertebrate species including barnacles and the horseshoe crab Limulus (7,8), whereas glycine and GABA 1 function as the inhibitory neurotransmitters in vertebrate phototransduction (9). Outside of phototransduction, histamine also appears to be the neurotransmitter in some mechanosensory neurons in Drosophila (10) and in lobster stomatogastric, cardiac, and olfactory neurons (11-13). To date, the molecular nature of the histamine receptor in these neurons is unknown. The laminar neurons that are postsynaptic to insect photoreceptors respond to light with a rapid, chloride-mediated hyperpolarization that can be mimicked by application of histamine (6). These laminar neurons were isolated from optic lobes of several insect species, and the hista...

) J. Biol. Chem. 272, 5157-5166]. Serine residue 890 in the C1 cassette is a primary target of PKC phosphorylation and a critical residue in receptor clustering at the membrane. We report herein that the presence of the C1 cassette reduces PKC potentiation and that mutation of Ser-890 significantly restores PKC potentiation. Splicing out or deletion of other C-terminal cassettes singly or in combination had little or no effect on PKC potentiation. Moreover, experiments involving truncation mutants reveal the unexpected finding that NMDARs assembled from subunits lacking all known sites of PKC phosphorylation can show PKC potentiation. These results indicate that PKC-induced potentiation of NMDAR activity does not occur by direct phosphorylation of the receptor protein but rather of associated targeting, anchoring, or signaling protein(s). PKC potentiation of NMDAR function is likely to be an important mode of NMDAR regulation in vivo and may play a role in NMDA-dependent long-term potentiation.excitatory amino acids ͉ site-directed mutagenesis N -methyl-D-aspartate receptors (NMDARs) mediate slow excitatory transmission in the brain and are thought to play a role in synaptogenesis, formation of neuronal circuitry, synaptic plasticity, and learning and memory (for review, see refs. 1 and 2). NMDARs in mammalian brain are encoded by a gene family comprised of the NR1 and NR2A-D genes (3). Alternative splicing of NR1 mRNA provides further molecular diversity of NMDARs (for review see ref. 4). Altogether, eight receptor splice variants are possible, at least seven of which are expressed in the central nervous system. The variants arise through the insertion or deletion of three short exon cassettes in the Nterminal (N1) and C-terminal (C1 and C2) domains. Splicing out of the exon segment encoding C2 removes a stop codon, resulting in an ORF that encodes an unrelated sequence C2Ј at the distal end of the C terminus. NR1 splice variants differ in their patterns of temporal and spatial expression (5, 6), their pharmacological properties (7-12), their ability to be phosphorylated by protein kinases (13,14), their efficiency of insertion at the cell surface (15), and their subcellular localization in heterologous expression systems (16).Target sites of kinase-induced phosphorylation have been identified on the NR1, NR2A, and NR2B subunits (13,14,17). Protein kinase C (PKC) phosphorylates serine residues 889, 890, and 896 within the C1 exon of the NR1 subunit; protein kinase A (PKA) phosphorylates serine residue 897 (14). The relation of PKC-induced phosphorylation of the NR1 and NR2 subunits to PKC-induced potentiation of NMDA channel activity is, however, unclear.A number of intracellular neuronal proteins, including members of the postsynaptic density 95 (PSD-95͞SAP90) subfamily of membrane-associated putative guanylate kinases, ␣-actinin, calmodulin, neurofilament protein NF-L, and yotiao bind via the C tails of NMDAR to mediate membrane targeting, attachment to the neuronal cytoskeleton, and stabilization of NMDARs (...

The Gold Standard for determining freely dissolved concentrations (C) of hydrophobic organic compounds in sediment interstitial water would be in situ deployment combined with equilibrium sampling, which is generally difficult to achieve. In the present study, ex situ equilibrium sampling with multiple thicknesses of silicone and in situ pre-equilibrium sampling with low density polyethylene (LDPE) loaded with performance reference compounds were applied independently to measure polychlorinated biphenyls (PCBs) in mesocosms with (1) New Bedford Harbor sediment (MA, U.S.A.), (2) sediment and biota, and (3) activated carbon amended sediment and biota. The aim was to cross validate the two different sampling approaches. Around 100 PCB congeners were quantified in the two sampling polymers, and the results confirmed the good precision of both methods and were in overall good agreement with recently published LDPE to silicone partition ratios. Further, the methods yielded C in good agreement for all three experiments. The average ratio between C determined by the two methods was factor 1.4 ± 0.3 (range: 0.6-2.0), and the results thus cross-validated the two sampling approaches. For future investigations, specific aims and requirements in terms of application, data treatment, and data quality requirements should dictate the selection of the most appropriate partitioning-based sampling approach.

Protein kinase C (PKC) potentiates NMDA receptors in hippocampal, trigeminal, and spinal neurons. Although PKC phosphorylates the NMDA receptor subunit NR1 at four residues within the C terminal splice cassette C1, the molecular mech- influx. Contrary to expectation, splicing out the two Cterminal splice cassettes of NR1 enhanced PKC potentiation in a manner independent of extracellular Ca 2ϩ . This observation indicates that PKC potentiation does not require phosphorylation of the C1 cassette of the NR1 subunit. PKC potentiation of NMDA receptors in vivo is likely to be affected by Ca 2ϩ amplification of the potentiated signal; the degree of amplification will depend in part on alternative splicing of the NR1 subunit, which is regulated developmentally and in a cell-specific manner.

Activated carbon‐amended bed sediments reduced total polychlorinated biphenyl (PCB) accumulation in 3 functionally different marine species, sandworms (Alitta virens), hard clams (Mercenaria mercenaria), and sheepshead minnows (Cyprinodon variegatus), during both clean and contaminated ongoing sediment inputs. Mesocosm experiments were conducted for 90 d to evaluate native, field‐aged bed sediment PCBs, and ongoing input PCBs added 3 times a week. Simulated in situ remediation applied an activated carbon dose equal to the native organic carbon content that was premixed into the bed sediment for 1 mo. The highest bioaccumulation of native PCBs was in worms that remained in and directly ingested the sediment, whereas the highest bioaccumulation of the input PCBs was in fish that were exposed to the water column. When periodic PCB‐contaminated sediment inputs were introduced to the water column, the activated carbon remedy had minimal effect on the input PCBs, whereas the native bed PCBs still dominated bioaccumulation in the control (no activated carbon). Therefore, remediation of only the local bedded sediment in environmental systems with ongoing contaminant inputs may have lower efficacy for fish and other pelagic and epibenthic organisms. While ongoing inputs continue to obscure remedial outcomes at contaminated sediment sites, the present study showed clear effectiveness of activated carbon amendment remediation on native PCBs despite these inputs but no remediation effectiveness for the input‐associated PCBs (at least within the present study duration). Environ Toxicol Chem 2019;38:2326–2336. Published 2019 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.