Influence of stimulation rate on Y1795C Isus. Experimental recordings of TTX-sensitive current (see Methods) are shown at high gain in cells expressing Y1795C mutant channels. Currents shown are in response to voltage pulses (500 milliseconds, –10 mV) applied from a holding potential of –100 mV. Y1795C Isus during the initial depolarizing pulse is shown in the top panel. Below are steady-state traces recorded after a train of depolarizing pulses with different interpulse intervals (t) to mimic bradycardia (left, t = 1 second) and tachycardia (right, t = 20 milliseconds).