Abstract
γ-Aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system, exerts its effect through the activation of GABA receptors. GABAA receptors are ligand-gated chloride channels composed of five subunit proteins. Mammals have 19 different GABAA receptor subunits (α1–6, β1–3, γ1–3, δ, ε, π, θ, and ρ1–3), the physiological properties of which have been assayed by electrophysiology. However, the evolutionary conservation of the physiological characteristics of diverged GABAA receptor subunits remains unclear. Zebrafish have 23 subunits (α1, α2a, α2b, α3–5, α6a, α6b, β1–4, γ1–3, δ, π, ζ, ρ1, ρ2a, ρ2b, ρ3a, and ρ3b), but the electrophysiological properties of these subunits have not been explored. In this study, we cloned the coding sequences for zebrafish GABAA receptor subunits and investigated their expression patterns in larval zebrafish by whole-mount in situ hybridization. We also performed electrophysiological recordings of GABA-evoked currents from Xenopus oocytes injected with one or multiple zebrafish GABAA receptor subunit cRNAs and calculated the half-maximal effective concentrations (EC50s) for each. Our results revealed the spatial expressions and electrophysiological GABA sensitivities of zebrafish GABAA receptors, suggesting that the properties of GABAA receptor subunits are conserved among vertebrates.
Highlights
Γ-Aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system of vertebrates, controls the excitability of neural networks mainly through G ABAA receptors[1]
We successfully cloned cDNAs for all zebrafish GABAA receptor subunits except for α2b from an RNA mixture extracted from a pool of 1–5 dpf zebrafish embryos/larvae
The α2b information has been removed from the National Center for Biotechnology Information (NCBI) annotation as it was presumably caused by an incorrect annotation of the last exon
Summary
Γ-Aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system of vertebrates, controls the excitability of neural networks mainly through G ABAA receptors[1]. 23 putative GABAA receptor subunits (eight α, four β, three γ, one δ, one π, one ζ, and five ρ) in the zebrafish genome[12] They investigated the transcript levels of G ABAA receptor subunits in the adult zebrafish brain using reverse transcription-polymerase chain reaction (RT-qPCR). We assayed GABA-mediated gating of zebrafish GABAA receptors composed of various combinations of receptor subunits in Xenopus oocytes. These attempts provide useful information on the spatial expressions and electrophysiological GABA sensitivities of zebrafish GABAA receptors and suggest that the properties of GABAA receptor subunits are conserved among vertebrates
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