Each test concentration was applied for 15?min and responses were measured at the last 2?min of the 15?min application. Parameters of cardiac haemodynamics, electrophysiology and the derivatives [HR, coronary perfusion pressure, left ventricle end diastolic pressure, LVDP, maximal +dP/dt and minimal �CdP/dt, RR interval, PR interval, QRS duration, QT interval and QTcF interval, monophasic action potential duration (MAPD) at 30%, 50% and 90% (MAPD30, MAPD50, MAPD90)] were monitored in real time and saved to hard drive continuously using Gould ACQ-7700 acquisition system and PONEMAH P3P software (Data Sciences International, St Paul, VRT752271 chemical structure
MN, USA). QT and MAPD90(cf, corrected by the sinus rate by Frederica formula) were used for assessing the delayed repolarization. Other parameters documented as sensitive indices for pro-arrhythmogenic potential of drugs, such as triangulation, reverse-use dependence, instability, transmural dispersion of repolarization (TDR), were analysed. Triangulation was calculated as the difference between MAPD90 and MAPD30 (MAPD90-30). Reverse-use dependence was determined by the slope of a liner-fitting over prolonged QT interval (% change from the pre-drug baseline level) obtained at spontaneous sinus rhythm, and when the heart was paced at 200 and 300 beats min?1, NVP-AUY922 mouse
respectively. TDR was measured by the duration of peak to end of the T Histamine H2 receptor
wave (Tp-e). The beat rate instability was quantified by the coefficient of variation (CV) of MAP beat-to-beat intervals. Thirty consecutive MAP beats during the last-minute of drug exposure were selected for CV calculation using the equation: CV (%) = SD/average of beat-to-beat intervals. The amount of test substance in the perfusate was measured by HPLC and actual concentrations are reported. Data are presented as mean �� SEM, and tabulated for each condition: control baseline, drug concentration and sinus rhythm/pacing frequency. Whenever applicable, changes in measured parameters were evaluated using one-way anova followed by Dunnett's multiple comparison test with JMP (Version 5.0.1, SAS Institute, Cary, NC, USA) to determine whether the change from baseline observed after equilibration in each drug concentration was significantly different (P < 0.05) from that observed in the time-matched vehicle control group. Whole-cell patch-clamp methods were used to record various channel currents from recombinant cells stably expressing human cardiac channels. An automated patch-clamp system was used to record various channel currents, except for experiments performed at physiological temperature (37?��?1��C) where conventional manual methods were employed. Cells were voltage-clamped using either the PatchXpress (PX) 7000A �C Automated Parallel Patch Clamp system (Molecular Devices, Inc.