Investigation into the mechanisms determining spontaneous activity in human-induced pluripotent stem cell-derived cardiomyocytes

Background: Human induced-pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) provide an alternative to adult primary cells for scientific and commercial research, but they have an embryonic rather than adult electrophysiological phenotype. In particular: low expression of inward rectifying channel (Ik1) contributes towards the unstable resting membrane potential and results in spontaneous electrical activity. Purpose: This study examines contribution of Ik1 and other ionic currents to the spontaneous electrical activity of hiPSC-CMs and tests the concept that additional external Ik1 activity can be added via co-culture with Ik1-expressing HEK293 cells. Methods: hiPSC-CM’s ionic currents and channels were investigated using different ion channel blockers. Ik1 was externally added to hiPSC-CM culture via co-culture with I¬k1-overexpressing HEK at different densities and ratios. The effects on contractility and voltage (action potentials) were investigated using two in-house platforms: CellOPTIQ and MUSCLEMOTION. Results: Based on the sensitivity to the If blocker, the pacemaker current (If) is either absent or not a dominant contributor to pacemaking in hiPSC-CMs. Blockade of Ik1 with BaCl2 and PA-6 did not affect interval time, thus showing that there is low availability of Ik1. Co-culture with Ik1-HEK at 1:1 HEK:hiPSC led to a prolongation of mean interval (from 963.524.5ms to 1516.079.3ms, n=15, p