identifying cardiac liabilities of new molecular entities early in drugdevelopment. Recently we have revealed that known cardiotoxicantswere associated with altered Ca2+i cycling in cultured guinea pigcardiomyocytes. Here we extended this study to the mouseembryonic stem cell-derived cardiomyocyte (Cor. At cells). Ca2+icycling in cultured Cor. At cells was monitored by Ca2+ imagingutilizing Fura-2 fluorescent dye. The effects of seven knowncardiotoxicants and one non-cardiotoxicant (amoxicillin) wereinvestigated and compared with effects previously observed incultured guinea pig cardiomyocytes. Whereas the alteration in Ca2+icycling induced by five of the seven cardiotoxicants in Cor. At cells wasidentical to that observed in guinea pig cardiomyocytes, Cor. At cellswere much less (~10 fold) sensitive to two cardiotoxicants, namelydofetilide and ouabain. As expected, amoxicillin did not interferewith Ca2+i cycling in either type of cardiomyocyte at concentrations upto 100 μM. These results confirm that the interruption of myocardialCa2+ iregulation can be closely linked to known cardiovascularliabilities, and support the notion of using myocardial Ca2+i analysisas a valuable tool to investigate drug-related cardiotoxicity. Further-more, the selection of cells with different phenotypes should beevaluated carefully to ensure the predictive power of in vitro drugsafety assessment.

doi:10.1016/j.vascn.2010.11.121

Poster Number: 118Board Number: 57

Multiple effects of Flecainide on the electrophysiology ofcardiomyocytes grown on microelectrode arraysSimon Bryant, Chris Wyllie, Rebecca Palmer, Richard Heal,Ricardo Davis, Julian Demmon, Scott Nicol

VivoMedica (UK) Ltd., London, United Kingdom

Flecainide (Flec), a class 1c antiarrhythmic exerts its antiarrhyth-mic effect primarily via sodium channel block but is also known toinhibit other ion channels including IKr. Single ion channel assaysmay not fully identify the effects of compounds that have actionson multiple ion channels. A novel assay using cardiomyocytes grownonto microelectrode arrays (MEA) may provide a better in vitroscreening tool for detecting drug-induced changes in cardiac electro-physiology. Aims: (1) Quantify Flec-induced changes in spontaneousfield action potentials (sfAP) using DrugPrint®; and (2) Compare theeffects of Flec with other know sodium and potassium channelblocking drugs. Methods: Embryonic rat cardiac myocytes werecultured onto MEAs (220/30ir-ITO-gr, MCS, Germany). Voltage signalswere recordedwith a 60-channel amplifier at 37 °C. Results: Flecainidecaused a concentration-dependent reduction in the amplitudes ofthe positive and negative components of the initial spike complex(from 748 to 532 μV, Flec 1.5 μM, P<0.001 and from 1392 to 1065 μV,Flec 1.5 μM, P=0.05 respectively) and a concentration-dependentprolongation of sfAP duration (from, 175 to 192 ms, Flec 1.5 μM,P<0.02). A small reduction in beat rate and conduction velocity wasalso observed. Conclusion: The effects of a low concentration of Flec onsfAP waveform profile are consistent with both sodium and potassiumchannel block. These data show that cardiomyocytes grown on MEAscombinedwith DrugPrint® analysis software provides an assay systemthat is able to discriminate between different modes of drug action.

doi:10.1016/j.vascn.2010.11.122

Poster Number: 119Board Number: 58

Electrophysiological effects of calcium channelantagonists, isradipine and nicardipine on cardiacaction potential repolarizationHyang-Ae Lee, Sung Gurl Park, Ki Suk Kim

Korea Institute of Toxicology, KRICT, Daejeon, Republic of Korea

Until recently, calcium channel blockers including isradipine andnicardipine have beenwidely used for cardiovascular diseases such ashypertension and ischemic heart disease. In this study, we investi-gated the electrophysiological effects of isradipine and nicardipine oncardiac repolarization using conventional microelectrode recordingtechniques in isolated rabbit Purkinje fibers and a whole-cell patchclamp technique in CHO cells stably expressed with hERG(IKr).Nicardipine inhibited the hERG current in a concentration-dependentmanner. The half-maximum inhibition concentration (IC50) wasapproxiamately 0.6 μM. However, isradipine at 30 μM shown only28.6% inhibition of hERG. In the APD assay, isradipine shortened theAPD50 in a dose-dependent manner. The effects were statisticallysignificant at concentrations of 1 and 30 μM, from 176.7±7.5 to120.0±18.0 ms (P<0.05) and from 176.7±7.5 to 88.2±0.2 ms(P<0.01). Isradipine at 30?μM significantly decreased the RMP from-86.4±2.5 to -75.8±0.9 mV (P<0.05) and Vmax from 276.3±24.2to 150.4±29.6 V/s (P<0.05), but not total amplitude (TA). Bycontrast, nicardipine only at a concentration of 30 μM significantlyshortened APD50 from 141.4±2.9 to 72.4±9.2 ms. Nicardipine at upto 30 μM did not affect any other AP parameters, APD90, RMP, Vmax

or TA. Based on the results, the APD shortening effect of isrdipine ismore strong than of nicardipine. But hERG blocking effect ofisradipine is less than of nicardipine. It is considered that thecalcium channel blocking effect would shorten QT intervals, whilethe hERG blocking effect would prolong the QT interval, thuscontributing to an attenuated QT prolongation. Several studiessuggested that a short QT interval could potentially increase the riskof sudden death. Therefore all patients taking this drugs should becautiously monitored for cardiac events.

doi:10.1016/j.vascn.2010.11.123

Poster Number: 120Board Number: 59

Use of multielectrode arrays (MEA) to evaluate proarrhythmicpotential of sodiumandherg channel inhibitors in rabbit sinoatrialnode tissue (SA)Hong Shi, Geoff Lewen, Jia Zhu, Huabin Sun, Paul Levesque

Bristol-Myers Squibb Company, Pennington, NJ, United States

The proarrhythmic activity of Na+ and hERG channel inhibitors wasevaluated under conditions mimicking systemic abnormal serum K+,a risk factor for proarrhythmia, using MEA technology and rabbitisolated SA tissue. SA node-atrial muscle preparation was isolated fromrabbit heart, placed on a 60 electrode MEA chip and superfused withoxygenated physiologic buffer (4 mM K+) at 35 °C. Spontaneous fieldpotentials (FP) were recorded every 5 min during 20–30 min drugtreatment. The Na+ channel inhibitors flecainide and lidocaine wereevaluated in high K+ buffer to mimic hyperkalemia which is known toaugment their proarrhythmic risk. Lidocaine (10 mM) delayed conduc-tion time (CT) by 207% in 8 mM K+ vs 54% in 4 mM K+ and elicited

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