Action potential experiments complete hERG assay and QT-interval measurements in cardiac preclinical studies.
BACKGROUND
The ICHS7B guideline focused on hERG and QT assays, although other factors have also been linked with the induction of severe arrhythmias. Thus, the aim of the present study was to demonstrate that two in vitro action potential recordings constitute convincing models of predictive drug-induced Torsades de pointes (TdP) and re-entry arrhythmias.


METHODS
The effects of D,L-sotalol, flecainide and quinidine were investigated on potassium (hERG) and sodium (Na(V)1.5) currents transfected in HEK-293 cells to determine the repercussion of the blockade of these currents on rabbit Purkinje fibre (PF) and atrial action potentials. Atrial conduction velocity was also investigated as a model of re-entry arrhythmias.


RESULTS
hERG channels were blocked by D,L-sotalol, quinidine and flecainide (IC(50): 69, 0.33 and 0.74 micromol/L, respectively). D,L-sotalol (30 micromol/L) induced reverse-use dependent increases in action potential duration (APD(90): +31.7% and +81.2% at 1 and 0.2 Hz) and triangulation (APD(90-40): +34.7% and +73.6% at 1 and 0.2 Hz) in PF but not in atria. Quinidine (10 micromol/L) also increased APD(90) (+14.5% and +68.5% at 1 and 0.2 Hz) and APD(90-40) (+73.3% and +152.1% at 1 and 0.2 Hz) in PF. Flecainide (10 micromol/L) shortened APD(90) in PF (-26.0% and - 22.2% at 1 and 0.2 Hz). Quinidine and flecainide blocked Na(V)1.5 channels by 32.3% and 73.1%, respectively, and produced decreases in dV/dt(max) which were more marked in atria (-20.4% and -31.9%) compared to PF (-12.8% and 22.4%) at 1 Hz. Finally, quinidine and flecainide decreased atrial conduction speed by 14.6% and 30.8%, respectively.


CONCLUSIONS
Results obtained with flecainide demonstrate that use of the hERG channel alone should not be considered as a useful single assay. Rabbit Purkinje fiber action potentials can be considered as a comparable model for detection of reverse-use dependent APD prolongation and triangulation whereas the rabbit atria can be considered as a useful model for detection of sodium channel blockade associated with decreases in dV/dt(max) and conduction velocity.
Ducroq
Joffrey
J
PhysioStim, Z.I. de Brénas-Lautrec, 81440 Lautrec, France. joffrey.ducroq@physiostim.com
Printemps
Richard
R
Guilbot
Stephanie
S
Gardette
Jean
J
Salvetat
Céline
C
Le Grand
Marie
M
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D016275:Atrial Function / Q000187:drug effects; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical / Q000379:methods; D051638:Ether-A-Go-Go Potassium Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D005260:Female; D005424:Flecainide / Q000494:pharmacology; D006321:Heart / Q000187:drug effects / Q000503:physiopathology*; D006325:Heart Atria / Q000187:drug effects; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis / Q000503:physiopathology*; D008962:Models, Theoretical; D011690:Purkinje Fibers / Q000187:drug effects / Q000502:physiology; D011802:Quinidine / Q000494:pharmacology; D011817:Rabbits; D015203:Reproducibility of Results; D013015:Sotalol / Q000494:pharmacology; D013997:Time Factors; D016171:Torsades de Pointes / Q000139:chemically induced / Q000175:diagnosis / Q000503:physiopathology; D014162:Transfection
D000889:Anti-Arrhythmia Agents; D051638:Ether-A-Go-Go Potassium Channels; D013015:Sotalol; D011802:Quinidine; D005424:Flecainide