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Figure 4 Composite data of the effect of isoproterenol in the LQT1, LQT2 and LQT3 models. In LQT1, isoproterenol (Iso) produced a persistent prolongation of the APD₉₀ of the M cell and of the QT interval (at both 2 and 10 min), whereas the APD₉₀ of the epicardial cell was always abbreviated, resulting in a persistent increase in TDR (A and B). In LQT2, isoproterenol initially prolonged (2 min) and then abbreviated the QT interval and the APD₉₀ of the M cell to the control level (10 min), whereas the APD₉₀ of epicardial cell was always abbreviated, resulting in a transient increase in TDR (C and D). In LQT3, isoproterenol produced a persistent abbreviation of the QT interval and the APD₉₀ of both M and epicardial cells (at both 2 and 10 min), resulting in a persistent decrease in TDR (E and F). *p < 0.0005 vs. control; p < 0.0005; p < 0.005; p < 0.05, vs. 293B, d-Sotalol (d-Sot) or ATX-II. APD₉₀ = action potential duration measured at 90% repolarization; LQT1, 2, 3 = long QT syndrome 1, 2, 3; TDR = transmural dispersion of repolarization.

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