Na⁺ blocks K⁺ current through KcsA with fast and slow kinetics. (A) Single-channel current recordings adapted from Thompson et al. (2009), illustrating the decrease in K⁺ current amplitude and the decrease in burst durations in the presence of intracellular Na⁺. (B) I-V curves from Nimigean and Miller (2002), showing the effect of Na⁺ on the K⁺ single-channel current amplitude (red). Control data (black) and ideal Woodhull (1973) block (dashed line). (C) Mean burst durations decrease with increasing Na⁺ and voltage. Adapted from Thompson et al. (2009).