Abstract
The immature electrophysiology of human-induced pluripotent stem cell-derived cardiomyocytes (hiCMs) complicates their use for therapeutic and pharmacological purposes. An insufficient inward rectifying current (IK1) and the presence of a funny current (if) cause spontaneous electrical activity. This study tests the hypothesis that the co-culturing of hiCMs with a human embryonic kidney (HEK) cell-line expressing the Kir2.1 channel (HEK-IK1) can generate an electrical syncytium with an adult-like cardiac electrophysiology. The mechanical activity of co-cultures using different HEK-IK1:hiCM ratios was compared with co-cultures using wildtype (HEK–WT:hiCM) or hiCM alone on days 3–8 after plating. Only ratios of 1:3 and 1:1 showed a significant reduction in spontaneous rate at days 4 and 6, suggesting that IK1 was influencing the electrophysiology. Detailed analysis at day 4 revealed an increased incidence of quiescent wells or sub-areas. Electrical activity showed a decreased action potential duration (APD) at 20% and 50%, but not at 90%, alongside a reduced amplitude of the aggregate AP signal. A computational model of the 1:1 co-culture replicates the electrophysiological effects of HEK–WT. The addition of the IK1 conductance reduced the spontaneous rate and APD20, 50 and 90, and minor variation in the intercellular conductance caused quiescence. In conclusion, a 1:1 co-culture HEK-IK1:hiCM caused changes in electrophysiology and spontaneous activity consistent with the integration of IK1 into the electrical syncytium. However, the additional electrical effects of the HEK cell at 1:1 increased the possibility of electrical quiescence before sufficient IK1 was integrated into the syncytium.
Highlights
Assuming the frequency of spontaneous electrical activity can be used as an assay of the influence of IK1 activity on coupled human embryonic kidney (HEK) cells, the spontaneous contractile activity of the co-culture of human-induced pluripotent stem cell-derived cardiomyocytes (hiCMs) with HEKs was investigated at different ratios of HEK:hiCM
This study was designed to investigate a method for reproducibly introducing a specific conductance (IK1 ) into a hiCM syncytium so as to generate an overall electrical behavior that would facilitate the use of hiCM tissues in cardio-toxicological screening and regenerative medicine
A feature of all hiCMs is spontaneous electrical activity due to a slowly depolarizing diastolic potential, which is thought to be a consequence of the significant expression of the funny current (If ) [1,7,8] and the lower expression of the IK1 current in these cells [1,3,9,10,11]
Summary
Human-induced pluripotent stem cell-derived cardiomyocytes (hiCMs) are a potential alternative to adult cardiomyocytes from animal models for pharmacotoxicity and regenerative medicine [1,2,3,4,5,6] This cell source could circumvent inter-species differences and provide human-translatable information [4,7]. HiCMs have been widely studied in recent years, and their electrical phenotype has been described as immature [3,7] This has been attributed in part to the expression of the pacemaker current (if) in hiCMs that are nominally ventricular in their electrical phenotype [1,7,8]. Strategies to overcome the lack of IK1 in hiCMs include the supplementation of ionic IK1 current with an electrical current of similar characteristics [7,16,17], but this cannot be applied to a monolayer or 3D culture
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