title: Distinct roles for two histamine receptors (hclA and hclB) at the Drosophila photoreceptor synapse.
abstract: Histamine (HA) is the photoreceptor neurotransmitter in arthropods, directly gating chloride channels on large monopolar cells (LMCs), postsynaptic to photoreceptors in the lamina. Two histamine-gated channel genes that could contribute to this channel in Drosophila are hclA (also known as ort) and hclB (also known as hisCl1), both encoding novel members of the Cys-loop receptor superfamily. Drosophila S2 cells transfected with these genes expressed both homomeric and heteromeric histamine-gated chloride channels. The electrophysiological properties of these channels were compared with those from isolated Drosophila LMCs. HCLA homomers had nearly identical HA sensitivity to the native receptors (EC(50) = 25 microM). Single-channel analysis revealed further close similarity in terms of single-channel kinetics and subconductance states ( approximately 25, 40, and 60 pS, the latter strongly voltage dependent). In contrast, HCLB homomers and heteromeric receptors were more sensitive to HA (EC(50) = 14 and 1.2 microM, respectively), with much smaller single-channel conductances ( approximately 4 pS). Null mutations of hclA (ort(US6096)) abolished the synaptic transients in the electroretinograms (ERGs). Surprisingly, the ERG "on" transients in hclB mutants transients were approximately twofold enhanced, whereas intracellular recordings from their LMCs revealed altered responses with slower kinetics. However, HCLB expression within the lamina, assessed by both a GFP (green fluorescent protein) reporter gene strategy and mRNA tagging, was exclusively localized to the glia cells, whereas HCLA expression was confirmed in the LMCs. Our results suggest that the native receptor at the LMC synapse is an HCLA homomer, whereas HCLB signaling via the lamina glia plays a previously unrecognized role in shaping the LMC postsynaptic response.
authors.affiliation: Department of Physiology, Development, and Neuroscience, University of Cambridge, Cambridge CB2 3DY, United Kingdom.
authors.forename: Antonios
authors.initials: A
authors.lastname: Pantazis
authors.forename: Ashvina
authors.initials: A
authors.lastname: Segaran
authors.forename: Che-Hsiung
authors.initials: CH
authors.lastname: Liu
authors.forename: Anton
authors.initials: A
authors.lastname: Nikolaev
authors.forename: Jens
authors.initials: J
authors.lastname: Rister
authors.forename: Andreas S
authors.initials: AS
authors.lastname: Thum
authors.forename: Thomas
authors.initials: T
authors.lastname: Roeder
authors.forename: Eugene
authors.initials: E
authors.lastname: Semenov
authors.forename: Mikko
authors.initials: M
authors.lastname: Juusola
authors.forename: Roger C
authors.initials: RC
authors.lastname: Hardie
mesh_terms: D000818:Animals; D002460:Cell Line; D018118:Chloride Channels / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D004330:Drosophila; D029721:Drosophila Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009457:Neuroglia / Q000502:physiology; D009899:Optic Lobe, Nonmammalian / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D018408:Patch-Clamp Techniques; D010775:Photic Stimulation / Q000379:methods; D017956:Photoreceptor Cells, Invertebrate / Q000166:cytology / Q000502:physiology*; D011968:Receptors, Histamine / Q000502:physiology*; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology
chemical_list: D018118:Chloride Channels; D029721:Drosophila Proteins; D009419:Nerve Tissue Proteins; D011968:Receptors, Histamine; C446763:ort protein, Drosophila