Figure 4. Onset of KvLQT1 channel inactivation is rapid and occurs without a delay when measured using a triple-pulse protocol.

A, currents recorded during a pulse to +40 mV, followed by a 20 ms interpulse to −130 mV, before a third pulse to a variable potential (+40 to −80 mV, applied in 10 mV decrements). Arrow indicates zero current. Inset shows expanded view of currents delineated by dotted box. B, I-V relationship for fully activated KvLQT1 channel current determined by extrapolating currents to the beginning of the test pulse (denoted by □, inset in A). Mean data were fitted with a straight line by linear regression (n = 4). C, voltage dependence of inactivation time constants obtained from single-exponential fits to decaying current traces.