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Syncytium cell growth increases Kir2.1 contribution in human iPSC-cardiomyocytes.

Authors
  • Li, Weizhen1
  • Han, Julie L1
  • Entcheva, Emilia1
  • 1 Department of Biomedical Engineering, George Washington University, Washington, District of Columbia.
Type
Published Article
Journal
AJP Heart and Circulatory Physiology
Publisher
American Physiological Society
Publication Date
Nov 01, 2020
Volume
319
Issue
5
Identifiers
DOI: 10.1152/ajpheart.00148.2020
PMID: 32986966
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) enable cardiotoxicity testing and personalized medicine. However, their maturity is of concern, including relatively depolarized resting membrane potential and more spontaneous activity compared with adult cardiomyocytes, implicating low or lacking inward rectifier potassium current (Ik1). Here, protein quantification confirms Kir2.1 expression in hiPSC-CM syncytia, albeit several times lower than in adult heart tissue. We find that hiPSC-CM culture density influences Kir2.1 expression at the mRNA level (potassium inwardly rectifying channel subfamily J member 2) and at the protein level and its associated electrophysiology phenotype. Namely, all-optical cardiac electrophysiology and pharmacological treatments reveal reduction of spontaneous and irregular activity and increase in action potential upstroke in denser cultures. Blocking Ik1-like currents with BaCl2 increased spontaneous frequency and blunted action potential upstrokes during pacing in a dose-dependent manner only in the highest-density cultures, in line with Ik1's role in regulating the resting membrane potential. Our results emphasize the importance of syncytial growth of hiPSC-CMs for more physiologically relevant phenotype and the power of all-optical electrophysiology to study cardiomyocytes in their multicellular setting.NEW & NOTEWORTHY We identify cell culture density and cell-cell contact as an important factor in determining the expression of a key ion channel at the transcriptional and the protein levels, KCNJ2/Kir2.1, and its contribution to the electrophysiology of human induced pluripotent stem cell-derived cardiomyocytes. Our results indicate that studies on isolated cells, out of tissue context, may underestimate the cellular ion channel properties being characterized.

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