ABSTRACT
Nineteen GABA(A) receptor (GABA(A)R) subunits are known in mammals with only a restricted number of functionally identified native combinations. The physiological role of beta1-subunit-containing GABA(A)Rs is unknown. Here we report the discovery of a new structural class of GABA(A)R positive modulators with unique beta1-subunit selectivity: fragrant dioxane derivatives (FDD). At heterologously expressed alpha1betaxgamma2L (x-for 1,2,3) GABA(A)R FDD were 6 times more potent at beta1- versus beta2- and beta3-containing receptors. Serine at position 265 was essential for the high sensitivity of the beta1-subunit to FDD and the beta1N286W mutation nearly abolished modulation; vice versa the mutation beta3N265S shifted FDD sensitivity toward the beta1-type. In posterior hypothalamic neurons controlling wakefulness GABA-mediated whole-cell responses and GABAergic synaptic currents were highly sensitive to FDD, in contrast to beta1-negative cerebellar Purkinje neurons. Immunostaining for the beta1-subunit and the potency of FDD to modulate GABA responses in cultured hypothalamic neurons was drastically diminished by beta1-siRNA treatment. In conclusion, with the help of FDDs we reveal a functional expression of beta1-containing GABA(A)Rs in the hypothalamus, offering a new tool for studies on the functional diversity of native GABA(A)Rs.
Subject(s)
Dioxanes/chemistry , Receptors, GABA-A/chemistry , Animals , Electrophysiology/methods , Hypothalamus/metabolism , Male , Mice , Neurochemistry/methods , Neurons/metabolism , Oocytes/metabolism , Protein Structure, Tertiary , Purkinje Cells/metabolism , RNA, Small Interfering/metabolism , Rats , Rats, Wistar , Xenopus laevisABSTRACT
A series of N-substituted aminomethylphenol derivatives was synthesized by reductive amination. To study the inhibitory potency of the target compounds at the murine GABA transporters (mGAT1-mGAT4), a [(3)H]GABA uptake test system in a 96-well format based on HEK cells stably expressing mGAT1-mGAT4 was established and validated. Inhibitory potencies at mGAT1-mGAT4 in the micromolar range and a slight subtype selectivity for mGAT3 were observed for the synthesized aminomethylphenol derivatives. Among the compounds investigated 5-n-dodecylaminomethyl-2-methoxyphenol (21) was found to be most potent with an IC(50) value at mGAT3 of about 3muM.
Subject(s)
Benzylamines/chemical synthesis , Benzylamines/pharmacology , GABA Uptake Inhibitors , Animals , Benzylamines/chemistry , Cell Line , GABA Plasma Membrane Transport Proteins/classification , GABA Plasma Membrane Transport Proteins/metabolism , Humans , Methylation , Mice , Molecular Structure , Structure-Activity Relationship , gamma-Aminobutyric Acid/metabolismABSTRACT
Searching for potent and subtype selective parent structures of the murine gamma-aminobutyric acid (GABA) transporter subtypes mGAT3 and mGAT4 a series of amino acids was characterised in a uniform [3H]GABA uptake test system based on transiently expressed mGAT1-4. From several potent inhibitors showing IC50 values at mGAT3 and mGAT4 in the low microM range cis-4-aminocrotonic acid and (RS)-2,3-diaminopropionic acid turned out to be most subtype selective for these transporters. With (RS)-isoserine--a compound unknown as GAT inhibitor until now--one of the most potent amino acids selectively inhibiting mGAT3 and mGAT4 was found. Furthermore, (2-amino-1,3-thiazol-4-yl)acetic acid was identified as the first parent structure exhibiting a clear, though still moderate, selective inhibition of GABA uptake at mGAT3.
