Figure 2. Concentration-response relationships for Zn2+ inhibition of GABA-activated conductances on α1β1 GABAA receptors.
A, left panel, normalized zinc concentration-inhibition curves were constructed for GABA at external pH 5.4, 7.4 and 9.4. For this and all subsequent zinc inhibition curves, the GABA-induced conductances were normalized to the response evoked by 10 μm GABA in the absence of zinc. All data were fitted according to the antagonist inhibition model (see Methods) and IC50 values determined (Table 1; n = 9). The points represent the means ± s.e.m. A, right panel and B, indicate GABA equilibrium concentration conductance curves constructed in the absence and presence of 1 μm zinc at pH 7.4 and 9.4, or 50 μm zinc at pH 5.4 and normalized to the response induced by 10 μm GABA in the absence of zinc at pH 7.4. The data were fitted with the logistic equation (see Methods; n = 18) and EC50 values and Hill coefficients determined (Tables 2 and 3).