Dissociation of Muscimol, SR 95531, and Strychnine from GABA_A and Glycine Receptors, Respectively, Suggests Similar Cooperative Interactions

Abstract

Binding to gamma-aminobutyric acid-A (GABAA) receptors was studied in synaptosomal membranes of rat brain. Dissociation of [3H]muscimol and the GABAA antagonist [3H]2-(3-carboxypropyl)-3-amino-6-p-methoxyphenylpyridazinium bromide ([3H]SR 95531) binding elicited by 100-fold dilution was accelerated by excess of GABA or SR 95531. Control dissociation might be retarded by rebinding. The contribution of a rapid first phase of dissociation of the agonist [3H]muscimol was preferentially enhanced by SR 95531. In contrast, the dissociation of [3H]SR 95531 binding was preferentially accelerated by GABA. These opposite preferential accelerations can be explained by negative heterotropic cooperativity and a reversed affinity relationship of agonists and antagonists to GABAA binding sites with different affinities. Modification of the membranes by p-diazobenzenesulfonic acid (DSA) selectively decreased the accelerating effect of GABA on the dissociation of [3H]SR 95531 binding. [3H]Strychnine binding was studied in a membrane preparation of rat spinal cord. The dissociation of the antagonist [3H]strychnine elicited by dilution was preferentially accelerated by glycine. Again, pretreatment with DSA decreased selectively this negative heterotropic (i.e., allosteric) interaction. Chemical modification by DSA might be attributed to tyrosine residues responsible for similar allosteric interactions for the GABA- and glycine-gated chloride channels.

Extrasynaptic δ‐GABAA receptors are high‐affinity muscimol receptors

“…4d). The binding affinities, number of [ 3 H]muscimol binding sites as well as binding kinetics are in the same range as found in the literature (Wang et al 1979;Agey and Dunn 1989;Maksay 1990;Negro et al 1995;Ebert et al 1999). However, because of the missing high-affinity d-receptors with slow kinetics, our association and dissociation rates in dKO fore/midbrain, dKO cerebellum, and recombinant a1b2c2 receptors are an exception as they were faster than all association rates in the former published studies.…”

“…The binding affinities, number of [ 3 H]muscimol binding sites as well as binding kinetics are in the same range as found in the literature (Wang et al . ; Agey and Dunn ; Maksay ; Negro et al . ; Ebert et al .…”

Pharmacological induction of skin pigmentation unveils the neuroendocrine circuit regulated by light

“…Together, these results show that melanotrope cells express both GlyRs and GABA A Rs. To distinguish between their involvement in the neuroendocrine circuit controlling α ‐MSH secretion, we analysed the level of skin pigmentation in stage 42 embryos treated either with SR95531, a GABA A R antagonist with little affinity for GlyR (Martin and Dunn, ), and strychnine, a GlyR antagonist (Maksay, ). SR95531 (100 μM) induced a dose‐dependent dispersion of melanin, while strychnine was without effect (Figure E).…”

γ‐aminobutyric acid‐mediated neurotransmission in cerebellar–hypothalamic circuit attenuates gastric mucosal injury induced by ischemia‐reperfusion

“…GABA, which is the chief inhibitory neurotransmitter, plays an important effect in regulating neuronal excitability throughout the nervous system. Growing evidences 35 support the notion that GABA and glycine were considered as major inhibitory neurotransmitter to hyperpolarize target neurons. Immunohistochemical labeling of glycine and GABA in the cerebellum, spinal cord, and brainstem 36,37 revealed the coexistence of these two amino acids in neuronal somata and boutons.…”