Enhanced Differentiation of Stem Cell Derived Cardiac Myocytes by Electronic Expression of IK1 Reveals an Atrial-Specific Kv1.5-Like Current

Abstract

Human induced pluripotent stem cell derived cardiac myocytes (h-iPSC-CMs) are a major advance in drug safety testing and research into human cardiac electrophysiology. However, these cells have potential limitations when used for quantitative action potential (AP) analysis. These cells are a mixture of atrial and ventricular cell types, which can be distinguished, to some extent, by action potential (AP) morphology. However, the spontaneous activity of h-iPSC-CMs results in parameter variability and anomalous pharmacological responses, leading to cell misidentification. The spontaneous behavior is largely due to the absence of an IK1 inwardly rectifying potassium channel (IK1).We examined the effect of using an in silico interface to electronically express this missing IK1. An in silico interface was developed to express synthetic IK1 in cells under whole cell voltage clamp using a variant of the dynamic clamp approach. Electronic IK1 expression resulted in a stable physiological resting potential, eliminated spontaneous activity, reduced spontaneous early and delayed after depolarizations, and decreased AP variability. Stimulated APs had a rapid upstroke and spike and dome morphology, and the readily recognizable repolarization attributes of ventricular and atrial cells. When examining the late components of outward current, we found that APs classified on the basis of AP morphology as “atrial-like” had a significantly larger sustained outward Kv1.5-like component at +50 mV than “ventricular-like” APs (in pA/pF: 1.76 ± 0.47 (n=6) vs. 0.74 ± 0.07 (n=7), p 0.4). These data indicate that h-IPSC-CM myocytes with synthetic expression of IK1 can easily be differentiated into ventricular-like and atrial-like myocytes by AP morphology, and that atrial-like cells exhibit an atrial-specific current.