DENTATE GYRUS BASKET CELL GABA(A) RECEPTORS ARE BLOCKED BY ZN2- AN IN-SITU PATCH-CLAMP AND SINGLE-CELL PCR STUDY( VIA CHANGES OF THEIR DESENSITIZATION KINETICS )

Although GABA type A receptors (GABA(A)Rs) in principal cells have bee n 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 ki netic, pharmacological, and structural properties of dentate gyrus bas ket cell GABA(A)Rs. Application of 1 mM GABA (100 msec) to nucleated p atches via a piezo-driven fast application device resulted in a curren t 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 de sensitization. Dose-response curves for the peak and the slow componen t yielded EC50 values of 139 and 24 mu M, respectively. Zn2+ caused a marked blocking effect on both the peak and the slow component via a n oncompetitive mechanism (IC50 values of 8 and 16 mu M). This led to an acceleration of the slow component as well as a prolongation of recov ery from desensitization. Zn2+ sensitivity was suggested to depend on the absence of gamma-subunits in GABA(A)Rs. To test this hypothesis we performed single-cell reverse transcription PCR that revealed primari ly the presence of alpha(2)-, beta(2)-, beta(3)-, gamma(1)-, and gamma (2)-subunit mRNAs. In addition, flunitrazepam increased the receptor a ffinity for its agonist, indicating the presence of functional benzodi azepine binding sites, i.e., gamma-subunits. Thus, additional factors seem to co-determine the Zn2+ sensitivity of native GABA(A)Rs. The mod ulatory effects of Zn2+ on GABA(A)R desensitization suggest direct inf luences on synaptic integration via changes in inhibition and shunting at GABAergic synapses.