Characterization of zebrafish GABA_A receptor subunits

γ-Aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system, exerts its effect through the activation of GABA receptors. GABA_A receptors are ligand-gated chloride channels composed of five subunit proteins. Mammals have 19 different GABA_A 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 GABA_A 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 GABA_A 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 GABA_A 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 GABA_A receptors, suggesting that the properties of GABA_A receptor subunits are conserved among vertebrates.