Identification of Two Novel Drosophila melanogaster Histamine-gated Chloride Channel Subunits Expressed in the Eye

Abstract

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...

The structural basis of function in Cys-loop receptors

“…There has already been considerable research on these receptors, and the more recent identification of new members (e.g. Histamine-gated (Beg & Jorgensen, 2003 ;Bocquet et al 2007 ;Davies et al 2002 ;Zheng et al 2002), EXP-1 (Beg & Jorgensen, 2003), Zinc-activated (Davies et al 2002), ELIC (Hilf & Dutzler, 2008), proton-gated (Bocquet et al 2007), glutamate-gated (Cully et al 1994, MOD-1 (Ranganathan et al 2000) and SsCl (Mounsey et al 2007)) suggests that others still remain undiscovered. A combination of traditional experimental methods and some of the more recent developments described in section 7 will provide us with further insights, many of which will be widely applicable to the whole Cys-loop receptor family.…”

“…Invertebrate receptors may also have multiple subunits ; several glutamate-gated and pHCl receptor subunits have been reported, although currently there are only two known histaminegated receptor subunits (HisCl1 and HisCl2SsCl) and single SsCl and MOD-1 receptor subunits (Cully et al 1996(Cully et al , 1994Mounsey et al 2007 ;Ranganathan et al 2000 ;Zheng et al 2002). Prokaryotic receptors discovered to date also only have single subunits, but as many of these have only recently been described, the diversity of their subunits types may grow with further investigation (Bocquet et al 2007 ;Hilf & Dutzler, 2008 ;Nury et al 2009).…”

Histamine and Its Receptors Modulate Temperature-Preference Behaviors inDrosophila

“…Compared with previous reports, we observed some unique features. (1) Gisselmann et al (2002) and Zheng et al (2002) showed that Ort and HisCl1 could be assembled into functional homomultimers or heteromultimers. They reported that the histamine binding affinity of the heteromultimeric receptors is higher than that of homomultimers.…”

Glutamate-gated Chloride Channels

“…Insect GluCls are also partly responsible for the insecticidal activity of fipronil, as this compound blocks these channels in addition to its action at GABA receptors (21,22). Histamine-gated chloride channels (HisCls) are also affected by the application of MLs and may contribute to their insecticidal activity (2,23,24).…”

“…In addition to the main topic of this minireview (glutamate), invertebrate CysLGCC can be gated by compounds such as histamine (1)(2)(3), serotonin (4), dopamine (5), and tyramine (6), and unlike vertebrates, acetylcholine and GABA act at both anion-and cation-gated channels (7,8). In addition, an insect chloride channel (pHCl) inhibited by protons is a member of the CysLGCC family (9).…”