Continuous veratridine-activated Na currents only weakly affect Na/K pump currents that decay by 70% to 90%. Na/K (or Li/K) pump currents were repeatedly activated for 20 s by applying 7 mM extracellular K. (A) With 35 mM Na and 70 mM K on the cytoplasmic side, 15 µM veratridine activates a 0.4 nA outward current. Small inward current deflections upon deactivating pump currents, marked by arrowheads, are consistent with a 10% depletion of subsarcolemmal Na by pump activity. However, the deflections do not change as current runs down, indicating that they are not caused by pump activity. (B) In the presence of 50 mM Li and no K on the cytoplasmic side, Li/K pump currents decay almost completely in the absence of veratridine and decay by ∼85% in the presence of veratridine. The veratridine-activated outward Li current, upon deactivating pump current, is unaffected by Li/K pump currents. (C) In the presence of 120 mM extracellular Na, 25 mM cytoplasmic Na and 90 mM extracellular K, 15 µM veratridine activates a 0.4 nA inward current that is unaffected by activating and deactivating Na/K pump currents. Arrows indicate the magnitudes of peak and steady-state pump current without veratridine. Peak and steady-state pump currents are increased by 8% and 24%, respectively, in the presence of inward current, consistent with an increase of Na by 4.3 mM (Lu et al., 2016).