Automated High Throughput Na+ Late Current Assay on QPatch HT Platform for CiPA28

In cardiac muscle, sustained inward Na+ currents, also known as late Na⁺ currents (I_Na-L), occur under physiological conditions during the cardiac Action Potential AP (AP). In addition to extending the plateau duration before AP recovery, an increased INa-L can lead to the development of various triggers and substrates (early after depolarization, EAD) for arrhythmogenesis. Inhibition of I_Na-L current can prevent proarrythmia by reducing or reversing EAD even in the presence of a prolonged QTc interval (e.g. Ranolazine).

Therefore, I_Na-L is one of the seven ion channels selected for
evaluation in the comprehensive in vitro proarrythmia assay (CiPA).

Eurofins is a contributor to the Ion-Channel Work-Group of the
FDA/HESI/CIPA initiative, supporting validation of automated high-throughput methods on the QPatch HT to support the program consortium. These methods measure 1) enhancement or 2) inhibition of I_Na-L current, using either step pulse or ramp pulse protocol and reference pharmacology, ATXII. Three key parameters, I_Na-L current, leak current, time-matched vehicle control were measured. The data generated in this study demonstrate that measuring I_Na-L current charge measurement is superior to measuring I_Na-L current amplitude for both test and ramp pulse. We investigated the effects of CiPA-28 compounds on I_Na-L at the EC₅₀ of ATXII (30nM). With the un-blinding of CiPA Phase I (12) compounds, Chlorpromazine, Diltiazem, and Mexiletine were identified as hits. Our results indicate that none of the CiPA-28 compounds potentiated the I_Na-L current.