Action Potential Morphology Measurement of Cardiac Cell Chamber Specific Cell Types of Stem Cell-Derived Cardiac Myocytes

Abstract

Cardiac myocytes derived from human induced pluripotent stem cells (h-iPSC-CMs) are a novel system for use in cardiac research and drug safety testing. Electrical and transcriptional characterization of suggests that h-iPSC-CMs are a mixed population of myocytes reflecting different regions of the heart. Accordingly, individual hiPSC-CMs have been described as nodal, atrial, or ventricular based on action potential (AP) morphology. The chamber specific categorization of hiPSC-CMs has been called into question as displaying an “immature phenotype” in large part due to their spontaneous activity and depolarized membrane potentials resulting from deficient expression of the inward rectifier current (IK1) This depolarized activity results in AP properties that can potentially leading to inconsistent AP properties and potential misidentification of cellular phenotype. We tested two AP morphology classification methods, one using spontaneous APs vs stimulated APs electronically expressing IK1 using dynamic clamp. The agreement between myocytes selected as atrial was only 38% and ventricular was 68% among spontaneous APs and hiPSC-CM + IK1. Ultra-rapid delayed rectifier channels (IKur) are selectively inhibited by 50 μmolar 4-aminopyridine (4AP) and preferentially expressed in atrial vs ventricular cells. Thus, ventricular cells are insensitive to 50 μM 4AP, while atrial cells are sensitive. We used 4AP as a probe for correct determination of cell type. We then sorted determination by method. Where there was agreement in the phenotype determination, ventricular-like myocytes were insensitive to 4AP and atrial cells showed a large increase in APD. Conversely, when there was disagreement with spontaneous versus +IK1 classification, 4AP sensitivity was consistent with the IK1 criteria and inconsistent with the spontaneous criteria. This suggests that a stable IK1 mediated resting potential is essential for distinguishing cell type based on AP morphology.