Towards automation of a valuable preclinical cardiac safety pharmacology assay: Evaluation of the effects of cardiac ion channel blockers on cardiac repolarisation in vitro.
BACKGROUND
Purkinje fibre repolarisation assays are valuable tools for identifying compounds which affect cardiac ion channels. The throughput of compound testing in this assay is low therefore we designed a novel recording system to improve screening and animal tissue usage efficiencies.


METHODS
The system was used to evaluate compounds using standard sharp microelectrode techniques. Animal tissue usage efficiencies were quantified by adding up the total number of Purkinje fibres from which recordings were attempted and dividing this by the number of experimental data sets generated, to arrive at a 'fibres per data set' ratio. Test compounds were dofetilide (3 x 10(-10) to 10(-8) M), cisapride (10(-8) to 3 x 10(-7) M), terodiline (10(-6) to 3 x 10(-5) M) and verapamil (3 x 10(-7) to 10(-5) M).


RESULTS
Using the novel modified system, 21 data sets were generated from 29 fibres, compared to 24 data sets from 41 fibres using the conventional manual recording system, demonstrating a 24% improvement in the efficiency of animal tissue usage. Comparing data from the manual and modified systems revealed differences in absolute values for all parameters including APD90 (308.73 +/- 9.97 ms, n = 24, compared to 275.27 +/- 8.25 ms, n = 21, respectively; P < 0.05). Differences in the magnitude of changes in action potential parameters between the systems were also evident for all compounds including terodiline (1 x 10(-5) M) which caused a -27.1 +/- 16.5% reduction in APD50 in the manual system, compared to a - 55.2 +/- 2.2% reduction in the modified system.


CONCLUSIONS
Although the value of the present study is limited by the small sample sizes, it has demonstrated utility of the modified system in improving efficiency of animal tissue usage. It offers potential utility in a higher throughput screening environment for examining the electrophysiological properties of novel compounds in native cardiac tissues, particularly where functional patch clamp data are limited.
Lightbown
Ian D
ID
Global Safety Pharmacology Group, Drug Safety Research & Development, Pfizer Global Research and Development (IPC 388), Ramsgate Road, Sandwich, Kent CT13 9NJ, United Kingdom. ian.lightbown@pfizer.com
Johnson
Mark
M
Davis
Anne
A
Leaney
Joanne
J
Leishman
Derek J
DJ
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D002082:Butylamines / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020117:Cisapride / Q000494:pharmacology; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical / Q000295:instrumentation / Q000379:methods; D004558:Electric Stimulation; D022062:Electrophysiologic Techniques, Cardiac / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000037:antagonists & inhibitors* / Q000502:physiology; D008133:Long QT Syndrome / Q000175:diagnosis / Q000503:physiopathology; D008297:Male; D008839:Microelectrodes; D010627:Phenethylamines / Q000494:pharmacology; D011690:Purkinje Fibers / Q000187:drug effects* / Q000502:physiology; D015203:Reproducibility of Results; D013449:Sulfonamides / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D000889:Anti-Arrhythmia Agents; D002082:Butylamines; D002121:Calcium Channel Blockers; D007473:Ion Channels; D010627:Phenethylamines; D013449:Sulfonamides; C010637:terodiline; D014700:Verapamil; C063533:dofetilide; D020117:Cisapride