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Dentate Gyrus Basket Cell GABA A Receptors Are Blocked by Zn 2+ via Changes of Their Desensitization Kinetics: An In Situ Patch-Clamp and Single-Cell PCR Study

1998; Society for Neuroscience; Volume: 18; Issue: 7 Linguagem: Inglês

10.1523/jneurosci.18-07-02437.1998

1529-2401

Thomas Berger, Cordelia S. Schwarz, Udo Kraushaar, Hannah Monyer,

Electrochemical Analysis and Applications

Although GABA type A receptors (GABA A Rs) in principal cells have been studied in detail, there is only limited information about GABA A Rs in interneurons. We have used the patch-clamp technique in acute rat hippocampal slices in combination with single-cell PCR to determine kinetic, pharmacological, and structural properties of dentate gyrus basket cell GABA A Rs. Application of 1 m m GABA (100 msec) to nucleated patches via a piezo-driven fast application device resulted in a current with a fast rise and a marked biexponential decay (time constants 2.4 and 61.8 msec). This decay could be attributed to strong receptor desensitization. Dose–response curves for the peak and the slow component yielded EC 50 values of 139 and 24 μ m , respectively. Zn 2+ caused a marked blocking effect on both the peak and the slow component via a noncompetitive mechanism (IC 50 values of 8 and 16 μ m ). This led to an acceleration of the slow component as well as a prolongation of recovery from desensitization. Zn 2+ sensitivity was suggested to depend on the absence of γ-subunits in GABA A Rs. To test this hypothesis we performed single-cell reverse transcription PCR that revealed primarily the presence of α 2 -, β 2 -, β 3 -, γ 1 -, and γ 2 -subunit mRNAs. In addition, flunitrazepam increased the receptor affinity for its agonist, indicating the presence of functional benzodiazepine binding sites, i.e., γ-subunits. Thus, additional factors seem to co-determine the Zn 2+ sensitivity of native GABA A Rs. The modulatory effects of Zn 2+ on GABA A R desensitization suggest direct influences on synaptic integration via changes in inhibition and shunting at GABAergic synapses.