- Email: [email protected]
Electrophysiologic and hemodynamic features in propofol-fentanyl anesthetized and conscious rabbits
Journal of Pharmacological and Toxicological Methods 58 (2008) 147–178
under isoflurane (2% in O2). Based on ECG obtained under isoflurane, we established a genotype specific heart-rate correction formula for the QT: WT: QTexp = 0.4 ⁎ RR + 92, LQT1: QTexp = 0.42 ⁎ RR +74, LQT2: QTexp = 0.65 ⁎ RR + 76. The QT-index (QTi) is defined as % of observed vs. expected QT. Results: Dofetilide led to a marked QTi prolongation in LQT1 rabbits. (LQT1, n = 7: baseline (%): 112 ± 11, at 4 min: 181 ± 14, at 8 min: 169 ± 6). Dofetilide prolonged QTi in WT rabbits to a lesser extent than in LQT1. (WT, n = 5: baseline (%): 108 ± 3, at 4 min: 131 ± 4, p = 0.01, at 8 min: 134 ± 5, p = 0.002). In contrast, no significant changes in QTi were observed in LQT2 rabbits indicating that they are insensitive to a selective IKr-blocker (LQT2, n = 9: baseline (%): 99 ± 8, at 4 min: 100 ± 9, at 8 min: 103 ± 8). Conclusion: IKr blocking drugs prolong the QTi in LQT1, but not in LQT2 rabbits. LQT1 rabbits are more sensitive to IKr blockers than WT rabbits. Thus, our transgenic LQT rabbits could serve as in vivo model system to selectively detect the IKr or IKs blocking propensity. doi:10.1016/j.vascn.2008.05.015 A novel analysis method for characterising in vitro cardioactive drug effects S. Bryant, S. Broadbent, C. Wyllie, W. Kotiadis, A. Parsons, R. Heal, J. Demmon, S. Nicol (Zi Medical plc, Sittingbourne, UK) Reliably detecting drug-induced changes in cardiac electrophysiology is an important feature of safety pharmacology. The use of cultured cardiac myocytes in conjunction with microelectrode arrays (MEAs) provides a novel in vitro screening tool for cardioactive drugs. Aims: The aims of this study were to: (1) validate a novel way of quantifying drug-induced changes in the spontaneous field potentials (sfAP) recorded from cardiac myocytes (DrugPrint™); (2) classify the effects of distinct classes of channel blockers on sfAP waveform, (3) assess the suitability of this bioassay system for profiling NCE's. Methods: Embryonic rat cardiac myocytes were cultured onto MEAs (220/30ir-ITO-gr, MCS, Germany). Voltage signals were recorded with a 60-channel amplifier at 37 °C, analysed offline. Results: Druginduced changes to the sfAP waveform were quantified using a series of mathematical analyses. For example ICa blockers (e.g., nifedipine) decreased the duration and profile area of the sfAP waveform causing a leftward shift in the centre of gravity. In contrast, IKr blockers (e.g., dofetilide) increased the duration of the sfAP waveform causing a right-shift in the centre of gravity. However INa blockers (e.g., lidocaine) primarily decreased spike amplitude without a significant effect on sfAP duration. Conclusion: These data demonstrate that drug-induced changes in sfAP corresponded to the known drug effects and that the specific mathematical descriptors used were able to discriminate between different modes of drug action These data suggest this is a suitable model for in vitro screening. doi:10.1016/j.vascn.2008.05.016 KCNA5-deficient mice do not have enhanced arrhythmia susceptibility Huabin Sun, Paul Levesque, Danshi Li (Bristol-Myers Squibb, Pennington, NJ, USA) A mouse EP model was developed to evaluate CV side effects of potential drug discovery targets using KO mice, and this is an example EP study. A loss-of-function mutation in KCNA5, which encodes the K channel Kv1.5 (IKur) in human atria, has been reported in an AF case. Kv1.5 encodes K currents in mouse atria and ventricles, and inhibition of Kv1.5 using pharmacologic or transgenic approaches produces
149
mixed, study-dependent effects on repolarization. We examined the role of Kv1.5 in atrial arrhythmogenesis using KCNA5 KO mice. Adult WT (n = 18) and Kv1.5 −/− KO (n = 23) mice were anesthetized and EP features were studied using an intra-atrial catheter and standard EP protocols. AF induction was performed +/−isoproterenol using triple extra stimulation and burst pacing. AF, defined as rapid irregular atrial rhythm lasting N0.1 s, was considered inducible if bursts or triple extra stimulation evoked an AF episode. trial ERP, HR and SNRT were not different between KO and WT mice. No spontaneous atrial or ventricular arrhythmias were observed in KO or WT mice. Burst pacing induced AF in 2/10 KO and 1/8 WT without iso, and in 4/10 KO and 5/8 WT with iso challenge. Iso increased AF duration (AFD) in both groups, but AFD under iso was longer in WT versus KO mice. There was no difference in AV node function (PR, AVN-ERP and Wenckebach CL), and iso induced more proarrhythmic activity in WT than in KO mice. This study, the first to examine the role of Kv1.5 in AF using a KO approach, indicates that loss of Kv1.5 does not enhance AF susceptibility and may in fact reduce it. doi:10.1016/j.vascn.2008.05.017 Electrophysiologic and hemodynamic features in propofol–fentanyl anesthetized and conscious rabbits Danshi Li, Huabin Sun, Paul Levesque (Bristol-Myers Squibb, Pennington, NJ, USA) Rabbits are commonly used for investigating the potential for drug induced effects on cardiac electrophysiology (EP), but there are no comparative EP and hemodynamic studies in anesthetized and conscious rabbit preparations. We evaluated cardiac EP and hemodynamic features in N100 propofol–fentanyl anesthetized and in 30 conscious rabbits. EP parameters were measured from surface ECG and from atrial and ventricular electrograms via intracardiac catheters using programmed electrical stimulation and a multi-channel mapping system. Arterial blood pressure (BP) and left ventricular pressure (LVP) were measured via an arterial catheter and a ventricular Millar catheter, respectively. BP, LVP and LV dP/dt were higher, and heart rate (HR) was faster in conscious versus anesthetized rabbits, consistent with cardiodepressent effects of anesthetics. Conscious rabbits had shorter PR, QRS and uncorrected QT intervals, consistent with a higher HR. Rate-corrected QT intervals and ventricular refractory period (VERP) were similar in conscious and anesthetized rabbits. The IKr inhibitor sotalol prolonged QTc, and the Na channel inhibitor flecainide widened QRS duration similarly in conscious and anesthetized rabbits. Sotalol had similar effects on refractory periods in both groups. Sinus node recovery time (SNRT), a measure of SA node function, was shorter in conscious rabbits, but the rate-corrected SNRT was similar between conscious and anesthetized rabbits. Baseline EP and ion channel pharmacology are similar in propofol–fentanyl anesthetized and conscious rabbits. doi:10.1016/j.vascn.2008.05.018 A canine model of relatively sustained atrial fibrillation induced by rapid atrial pacing and phenylephrine Anusak Kijtawornrat, Brian M. Roche, Jennifer L. Lolly, Robert L. Hamlin (QTest Labs, LLC /Ohio State University/Chulalongkorn University, Columbus, Ohio, USA) Atrial fibrillation is a common arrhythmia with important morbidity and mortality. Limitations in studying both mechanisms and therapy arise for paucity of models that possess a high yield, are
under isoflurane (2% in O2). Based on ECG obtained under isoflurane, we established a genotype specific heart-rate correction formula for the QT: WT: QTexp = 0.4 ⁎ RR + 92, LQT1: QTexp = 0.42 ⁎ RR +74, LQT2: QTexp = 0.65 ⁎ RR + 76. The QT-index (QTi) is defined as % of observed vs. expected QT. Results: Dofetilide led to a marked QTi prolongation in LQT1 rabbits. (LQT1, n = 7: baseline (%): 112 ± 11, at 4 min: 181 ± 14, at 8 min: 169 ± 6). Dofetilide prolonged QTi in WT rabbits to a lesser extent than in LQT1. (WT, n = 5: baseline (%): 108 ± 3, at 4 min: 131 ± 4, p = 0.01, at 8 min: 134 ± 5, p = 0.002). In contrast, no significant changes in QTi were observed in LQT2 rabbits indicating that they are insensitive to a selective IKr-blocker (LQT2, n = 9: baseline (%): 99 ± 8, at 4 min: 100 ± 9, at 8 min: 103 ± 8). Conclusion: IKr blocking drugs prolong the QTi in LQT1, but not in LQT2 rabbits. LQT1 rabbits are more sensitive to IKr blockers than WT rabbits. Thus, our transgenic LQT rabbits could serve as in vivo model system to selectively detect the IKr or IKs blocking propensity. doi:10.1016/j.vascn.2008.05.015 A novel analysis method for characterising in vitro cardioactive drug effects S. Bryant, S. Broadbent, C. Wyllie, W. Kotiadis, A. Parsons, R. Heal, J. Demmon, S. Nicol (Zi Medical plc, Sittingbourne, UK) Reliably detecting drug-induced changes in cardiac electrophysiology is an important feature of safety pharmacology. The use of cultured cardiac myocytes in conjunction with microelectrode arrays (MEAs) provides a novel in vitro screening tool for cardioactive drugs. Aims: The aims of this study were to: (1) validate a novel way of quantifying drug-induced changes in the spontaneous field potentials (sfAP) recorded from cardiac myocytes (DrugPrint™); (2) classify the effects of distinct classes of channel blockers on sfAP waveform, (3) assess the suitability of this bioassay system for profiling NCE's. Methods: Embryonic rat cardiac myocytes were cultured onto MEAs (220/30ir-ITO-gr, MCS, Germany). Voltage signals were recorded with a 60-channel amplifier at 37 °C, analysed offline. Results: Druginduced changes to the sfAP waveform were quantified using a series of mathematical analyses. For example ICa blockers (e.g., nifedipine) decreased the duration and profile area of the sfAP waveform causing a leftward shift in the centre of gravity. In contrast, IKr blockers (e.g., dofetilide) increased the duration of the sfAP waveform causing a right-shift in the centre of gravity. However INa blockers (e.g., lidocaine) primarily decreased spike amplitude without a significant effect on sfAP duration. Conclusion: These data demonstrate that drug-induced changes in sfAP corresponded to the known drug effects and that the specific mathematical descriptors used were able to discriminate between different modes of drug action These data suggest this is a suitable model for in vitro screening. doi:10.1016/j.vascn.2008.05.016 KCNA5-deficient mice do not have enhanced arrhythmia susceptibility Huabin Sun, Paul Levesque, Danshi Li (Bristol-Myers Squibb, Pennington, NJ, USA) A mouse EP model was developed to evaluate CV side effects of potential drug discovery targets using KO mice, and this is an example EP study. A loss-of-function mutation in KCNA5, which encodes the K channel Kv1.5 (IKur) in human atria, has been reported in an AF case. Kv1.5 encodes K currents in mouse atria and ventricles, and inhibition of Kv1.5 using pharmacologic or transgenic approaches produces
149
mixed, study-dependent effects on repolarization. We examined the role of Kv1.5 in atrial arrhythmogenesis using KCNA5 KO mice. Adult WT (n = 18) and Kv1.5 −/− KO (n = 23) mice were anesthetized and EP features were studied using an intra-atrial catheter and standard EP protocols. AF induction was performed +/−isoproterenol using triple extra stimulation and burst pacing. AF, defined as rapid irregular atrial rhythm lasting N0.1 s, was considered inducible if bursts or triple extra stimulation evoked an AF episode. trial ERP, HR and SNRT were not different between KO and WT mice. No spontaneous atrial or ventricular arrhythmias were observed in KO or WT mice. Burst pacing induced AF in 2/10 KO and 1/8 WT without iso, and in 4/10 KO and 5/8 WT with iso challenge. Iso increased AF duration (AFD) in both groups, but AFD under iso was longer in WT versus KO mice. There was no difference in AV node function (PR, AVN-ERP and Wenckebach CL), and iso induced more proarrhythmic activity in WT than in KO mice. This study, the first to examine the role of Kv1.5 in AF using a KO approach, indicates that loss of Kv1.5 does not enhance AF susceptibility and may in fact reduce it. doi:10.1016/j.vascn.2008.05.017 Electrophysiologic and hemodynamic features in propofol–fentanyl anesthetized and conscious rabbits Danshi Li, Huabin Sun, Paul Levesque (Bristol-Myers Squibb, Pennington, NJ, USA) Rabbits are commonly used for investigating the potential for drug induced effects on cardiac electrophysiology (EP), but there are no comparative EP and hemodynamic studies in anesthetized and conscious rabbit preparations. We evaluated cardiac EP and hemodynamic features in N100 propofol–fentanyl anesthetized and in 30 conscious rabbits. EP parameters were measured from surface ECG and from atrial and ventricular electrograms via intracardiac catheters using programmed electrical stimulation and a multi-channel mapping system. Arterial blood pressure (BP) and left ventricular pressure (LVP) were measured via an arterial catheter and a ventricular Millar catheter, respectively. BP, LVP and LV dP/dt were higher, and heart rate (HR) was faster in conscious versus anesthetized rabbits, consistent with cardiodepressent effects of anesthetics. Conscious rabbits had shorter PR, QRS and uncorrected QT intervals, consistent with a higher HR. Rate-corrected QT intervals and ventricular refractory period (VERP) were similar in conscious and anesthetized rabbits. The IKr inhibitor sotalol prolonged QTc, and the Na channel inhibitor flecainide widened QRS duration similarly in conscious and anesthetized rabbits. Sotalol had similar effects on refractory periods in both groups. Sinus node recovery time (SNRT), a measure of SA node function, was shorter in conscious rabbits, but the rate-corrected SNRT was similar between conscious and anesthetized rabbits. Baseline EP and ion channel pharmacology are similar in propofol–fentanyl anesthetized and conscious rabbits. doi:10.1016/j.vascn.2008.05.018 A canine model of relatively sustained atrial fibrillation induced by rapid atrial pacing and phenylephrine Anusak Kijtawornrat, Brian M. Roche, Jennifer L. Lolly, Robert L. Hamlin (QTest Labs, LLC /Ohio State University/Chulalongkorn University, Columbus, Ohio, USA) Atrial fibrillation is a common arrhythmia with important morbidity and mortality. Limitations in studying both mechanisms and therapy arise for paucity of models that possess a high yield, are