Block of Na⁺ gating pore currents in R666G by Zn²⁺. (A) Gating pore current in a representative cell recorded from a holding potential of −80 mV first in 120 mM Na⁺, 1.8-mM Ca²⁺ external solution (left, black traces), and after addition of 2.5 mM ZnSO₄ (right, red traces). (B) Concentration dependence of gating pore current block by Zn²⁺ assessed at a −80-mV holding potential (open circles, individual experiments; closed triangles, mean, n = 5). The solid red line is a fit of the averaged data with the Hill equation: rate= 1.3 ± 0.3, IC₅₀ = 0.36 ± 0.07 mM. (C) Representative gating pore currents recorded with a −120-mV holding potential in 120 mM Na⁺, 1.8-mM Ca²⁺ external solution (left, black traces), and after addition of 143 µM ZnSO₄ (right, blue traces). (D) Normalized leak-subtracted current-voltage relationships for Na⁺ gating pore currents recorded with a −120-mV holding potential in control 1.8Ca external solution (black circles, n = 6) and in the presence of 143 µM Zn²⁺ (blue diamonds, n = 6). Error bars represent SEM.