Figure 4.

Block of Na⁺ gating pore currents in R666G by Ba²⁺. (A) Gating pore current in a representative cell recorded from a holding potential of 0 mV in external solution containing 120 mM Na⁺ or 1.8 mM Ca²⁺ (black traces) and again after addition of 2.5 mM BaCl₂ (red traces). (B) Steady-state inhibition of gating pore currents by 2.5 mM Ba²⁺ assessed by plotting gating pore current amplitude versus gating charge for currents measured during a test pulse to −160 mV from a holding potential of 0 mV in either 1.8Ca solution (black circles) or a 1.5-mM Ca²⁺ + 2.5-mM Ba²⁺ solution (red triangles). Each symbol represents an individual oocyte. Data were fitted with linear function with zero intercept and slopes k_Ca = 490 ± 11 nA/nC and k_Ba = 290 ± 6 nA/nC. (C) Averaged current-voltage plots for gating currents measured from a holding potential of 0 mV in either 1.8-mM Ca²⁺ solution (black circles, n = 16) or a 1.5-mM Ca²⁺ + 2.5-mM Ba²⁺ solution (red triangles, n = 14). (D) Effect of chelation of Ba²⁺ with EDTA. Gating pore currents in a representative cell were first recorded in a 1.5-mM Ca²⁺ + 2.5-mM Ba²⁺ external solution (red triangles) and then after addition of 4 mM EDTA to external solution (blue squares). (E) Averaged current-voltage plots for gating currents measured from a holding potential of −100 mV in either a 1.8-mM Ca²⁺ solution (open black circles, n = 10) or 1.5-mM Ca²⁺ + 2.5-mM Ba²⁺ solution (open red triangles, n = 9).