Figure 7. Voltage dependence of divalent cation block.

A, representative I–V curves obtained at 0.5 and 5 mm Ba²⁺ in the extracellular solution. Note that in 5 mm Ba²⁺ the nAChR passes much less inward than outward current. B, the ratio of chord conductance in 5 mm Ba²⁺ with respect to that in 0.5 mm Ba²⁺ plotted against membrane voltage, shows that block by Ba²⁺ is much more effective at hyperpolarized than at depolarized potentials. The break in the x-axis corresponds to the data points that are close to or at the reversal potentials for the currents through the nAChR in 0.5 and 5 mm Ba²⁺. C, the ratio of current amplitudes at depolarized potentials (+43 mV) with respect to that at hyperpolarized potentials (−107 mV) shows that outward rectification is significantly higher in ACh-evoked currents elicited in the presence of 5 mm Ba²⁺ than those obtained in 0.5 mm Ba²⁺. Data were pooled from 12 to 14 IHCs.