Zinc Inhibits the GABA(A)R/ATPase during Postnatal Rat Development: The Role of Cysteine Residue

Zinc ions (Zn(2+)) are concentrated in various brain regions and can act as a neuromodulator, targeting a wide spectrum of postsynaptic receptors and enzymes. Zn(2+) inhibits the GABA(A)Rs, and its potency is profoundly affected by the subunit composition and neuronal developmental stage. Although the extracellular amino acid residues of the receptor’s hetero-oligomeric structure are preferred for Zn(2+) binding, there are intracellular sites that, in principle, could coordinate its potency. However, their role in modulating the receptor function during postembryonic development remains unclear. The GABA(A)R possesses an intracellular ATPase that enables the energy-dependent anion transport via a pore. Here, we propose a mechanistic and molecular basis for the inhibition of intracellular GABA(A)R/ATPase function by Zn(2+) in neonatal and adult rats. The enzymes within the scope of GABA(A)R performance as Cl(−)ATPase and then as Cl(−), HCO(3)(−)ATPase form during the first week of postnatal rat development. In addition, we have shown that the Cl(−)ATPase form belongs to the β1 subunit, whereas the β3 subunit preferably possesses the Cl(−), HCO(3)(−)ATPase activity. We demonstrated that a Zn(2+) with variable efficacy inhibits the GABA(A)R as well as the ATPase activities of immature or mature neurons. Using fluorescence recording in the cortical synaptoneurosomes (SNs), we showed a competitive association between Zn(2+) and NEM in parallel changes both in the ATPase activity and the GABA(A)R-mediated Cl(−) and HCO(3)(−) fluxes. Finally, by site-directed mutagenesis, we identified in the M3 domain of β subunits the cysteine residue (C313) that is essential for the manifestation of Zn(2+) potency.