A, family of current traces recorded from WT HERG, HERGNΔ12CΔ236, HERGNΔ12CΔ278, HERGNΔ354CΔ236, HERGNΔ354CΔ278, HERGNΔ12 and HERGNΔ354 are shown. Inactivation pulse protocol consisted of a pulse to +60 mV for 5 s with a subsequent pulse to −80 mV and a range of depolarizing potentials from +60 to −20 mV. B, inactivation time constants of WT HERG, HERGNΔ12CΔ236, HERGNΔ12CΔ278, HERGNΔ354CΔ236, HERGNΔ354CΔ278, HERGNΔ12 and HERGNΔ354 were plotted against test voltage (n = 20, P = 0.0004). Symbols are defined in the figure. Inactivation was slower in deletion mutants than in WT channels.