LAUSR

The hiPSCD-CM system provides a unique way to examine cardiac repolarization. However, the lack of, or low, expression endogenous IK1 results in spontaneous behavior that interferes with measurement of action potential (AP) parameters such as resting membrane potential (VM) and AP duration (APD). We electronically expressed IK1 via dynamic clamp in hiPSCD-CM. hiPSCD-CMs (iCell, Inc., WI) were studied using the Amphotericin B perforated patch technique. APs were triggered by a 1.5-2.0 nA pulse for 1.5 ms at 0.5 Hz. In the absence of electronically added IK1 the diastolic potential VM was unstable (VM varied from −70 to −20 mV, depending on the presence of spontaneous AP activity). APs measured in the absence of added IK1 had APD30: 191±57 ms, APD50: 255±61 ms, and APD90: 766±221 ms (mean±sd). The electronic addition of IK1 resulted in highly-stable APs with a steady VM of −84 mV and APD30: 212±29 ms, APD50: 274±38 ms, and APD90: 321±61 ms (mean±sd). In the presence of IK1, exposure to 1420 nM dofetilide produced the expected prolongation of the APD compared to control (APD90: 321±61 ms (control) vs. 420±21 ms (dofetilide)) with no change in VM (−84±0.2 mV (control) vs. −84±0.3 mV (dofetilide)). In contrast, in the absence of IK1, 1420 nM dofetilide resulted in depolarization of the resting membrane potential (−58±16 mV (control) vs. −24±4 mV (dofetilide)) and an unexpected shortening of the action potential (APD90: 766±221 ms (control) vs. 48±10 ms (dofetilide)). These data are consistent with our previous findings that lack of IK1 can result in an anomalous shortening of the AP when exposed to BayK-8644, which can be resolved by electronic expression of IK1.