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Figure 1 Effect of isoproterenol in the LQT1 model. Shown are superimposed action potentials recorded simultaneously from M and epicardial cells, together with a transmural ECG. BCL = 2,000 ms. Chromanol 293B (30 µmol/L) produced a homogeneous prolongation of APD of both cell types with no major change in the width of the T wave or in TDR. Isoproterenol (Iso, 100 nmol/L) in the continued presence of 293B dramatically prolonged the APD of the M cell (2 min) and maintained it prolonged as the effect approached a steady state (10 min), whereas the epicardial action potential was always abbreviated, resulting in a persistent increase in TDR and in a widening of the T wave, as commonly seen in LQT1 patients. APD = action potential duration; LQT1 = long QT syndrome 1; TDR = transmural dispersion of repolarization.
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