Figure 8. Block of hNav1.5-CW Na⁺ channels by Class 1a antiarrhythmic drugs. Superimposed Na⁺ current traces were recorded before and after the application of disopyramide (A) or quinidine (B) at concentrations ranging from 3.0 to 300 μM. Currents of hNav1.5-CW Na⁺ channels were evoked every 30 seconds by a 100-ms test pulse at +50 mV. Drugs were applied externally. The currents were recorded after the block reached its steady-state, usually within 3 min. A different cell was used in each panel. Holding potential was set at −140 mV. Traces of the control (0 μM), 10 and 100 μM drug concentrations are labeled.