Dear Editor, Loss-of-function and gain-of-function mutations in the KCNH2 gene cause long and short-QT syndromes (LQTS or SQTS), respectively, predisposing to life-threatening F I G U R E 1 Repolarization power of wild-type (WT) hERG as a function of temperature. A simplified and optimized action potential was applied (AP-clamp) by an automated patch clamp system in 384-well plates on HEK293 cells stably expressing hERG. (A) Mean (± SEM) current recordings during AP-clamp at various temperatures (in pA, n = 194, 211, 114 and 172 cells at 22-37 • C, respectively). Dashed line: AP time course (voltage scale: right Y axis). (B) Mean (± SEM) current recordings during AP-clamp at 27 • C for AP of various durations (see inset for APs; for currents: n = 168−254 for Time x 0.5 to x 5). The small inward current observed in (A) and (B), when the AP is returning to resting values, is attributed to contamination of the intracellular solution by the extracellular Tyrode solution, intrinsic to the cell catch process in the automated patch clamp (see supplementary information). (C) Mean (± SEM) time integral of the recorded currents: repolarization power, at various temperatures versus time factor (n = 155−232, 168−254, 79−133 and 144−173 at 22-37 • C, respectively). Horizontal dashed line: repolarization power at 37 • C: 22.3 pA.s. (D) As in (B), at 27 • C, after time and current corrections using various factors from 1.5 to 3 on the respective recordings. For example, for the recordings obtained during the AP of 2 x duration, the time was divided by 2 and the current multiplied by 2. Note the overlap of the current corrected by the factor of 2 at 27 • C (black) with the reference current obtained during the standard AP at 37 • C (red).