Syncytium cell growth increases IK1 contribution in human iPS-cardiomyocytes

Abstract

Human induced pluripotent stem-cell-derived cardiomyocytes (hiPS-CMs) enable cardiotoxicity testing and personalized medicine. However, their maturity is of concern, including relatively depolarized resting membrane potential and more spontaneous activity compared to adult cardiomyocytes, implicating low or lacking inward-rectifier potassium current (Ik1). Here, protein quantification confirms Ik1 expression in hiPS-CM syncytia, albeit several times lower than in adult heart tissue. We find that hiPS-CM cell culture density influences Ik1 expression and the associated electrophysiology phenotype. All-optical cardiac electrophysiology and pharmacological treatments reveal reduction of spontaneous and irregular activity in denser cultures. Blocking Ik1 with BaCl 2 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 hiPS-CM for more physiologically-relevant phenotype and the power of alloptical electrophysiology to study cardiomyocytes in their multicellular setting.

All-Optical Electrophysiology Refines Populations of In Silico Human iPSC-CMs for Drug Evaluation

“…One possibility is the lower temperature, though temperature-corrected in silico hiPSC-CMs revealed repolarization abnormalities. Another reason could be potentially higher I K1 (and/or I Ks ) in our high-density syncytial preparations compared to other studies ( 54 ).…”

Optogenetic currents in myofibroblasts acutely alter electrophysiology and conduction of co-cultured cardiomyocytes

“…Some studies used FRAP as evidence of diffusional (and therefore presumably electrical) coupling between CMs and MFBs [17], but these cannot be translated to a value of electrical conductance [37] or show that the connection is strong enough to cause significant slowing. Dual-cell patch clamp has been used to quantify the electrical connection between CM and MFB pairs [14,38], but not in a syncytium, which allows for measurement of macroscopic CV, and has different electrophysiology than single cells [39]. Furthermore, dual-cell patch clamp measures conductance between cells next to each other, where due to the small height of cells relative to area only a small fraction of the cell surface is available for connection, although this is not the case for cells in 3-D tissue.…”