Persistent human cardiac Na+ currents in stably transfected mammalian cells: Robust expression and distinct open-channel selectivity among Class 1 antiarrhythmics.

Miniature persistent late Na+ currents in cardiomyocytes have been linked to arrhythmias and sudden death. The goals of this study are to establish a stable cell line expressing robust persistent cardiac Na+ currents and to test Class 1 antiarrhythmic drugs for selective action against resting and open states. After transient transfection of an inactivation-deficient human cardiac Na+ channel clone (hNav1.5-CW with L409C/A410W double mutations), transfected mammalian HEK293 cells were treated with 1 mg/ml G-418. Individual G-418-resistant colonies were isolated using glass cylinders. One colony with high expression of persistent Na+ currents was subjected to a second colony selection. Cells from this colony remained stable in expressing robust peak Na+ currents of 996 +/- 173 pA/pF at +50 mV (n = 20). Persistent late Na+ currents in these cells were clearly visible during a 4-second depolarizing pulse albeit decayed slowly. This slow decay is likely due to slow inactivation of Na+ channels and could be largely eliminated by 5 M batrachotoxin. Peak cardiac hNav1.5-CW Na+ currents were blocked by tetrodotoxin with an IC50 value of 2.27 +/- 0.08 M (n = 6). At clinic relevant concentrations, Class 1 antiarrhythmics are much more selective in blocking persistent late Na+ currents than their peak counterparts, with a selectivity ratio ranging from 80.6 (flecainide) to 3 (disopyramide). We conclude that (1) Class 1 antiarrhythmics differ widely in their resting- vs. open-channel selectivity, and (2) stably transfected HEK293 cells expressing large persistent hNav1.5-CW Na+ currents are suitable for studying as well as screening potent open-channel blockers.