Clustered and non-clustered GABAA receptors in cultured hippocampal neurons

In cultured hippocampal neurons, gamma(2) subunit-containing GABA(A)Rs form large postsynaptic clusters at GABAergic synapses and small clusters outside GABAergic synapses. We now show that a pool of non-clustered gamma(2) subunit-containing GABAARs are also present at the cell surface. We also demonstrate that myc- or EGFP-tagged gamma(2), alpha(2), beta(3) or alpha(1) subunits expressed in these neurons assemble with endogenous subunits, forming GABA(A)Rs that target large postsynaptic clusters, small clusters outside GABAergic synapses or a pool of non-clustered surface GABA(A)Rs. In contrast, myc- or EGFP-tagged delta subunits only form non-clustered GABA(A)Rs, which can be induced to form clusters by antibody capping. A nryc-tagged chimeric gamma(2) subunit possessing the large intracellular loop (IL) of the delta-subunit IL ((myc)gamma S-2/delta-IL) assembled into GABA(A)Rs, but it did not form clusters, therefore behaving like the 8 subunit. Thus, the large intracellular loops of gamma(2) and 6 play an important role in determining the synaptic clustering/non-clustering capacity of the GABA(A)Rs. (C) 2005 Elsevier Inc. All rights reserved.