Ion channelopathies in human induced pluripotent stem cell derived cardiomyocytes: a dynamic clamp study with virtual I-K1

Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) are widely used in studying basic mechanisms of cardiac arrhythmias that are caused by ion channelopathies. Unfortunately, the action potential profile of hiPSC-CMs and consequently the profile of individual membrane currents active during that action potential differs substantially from that of native human cardiomyocytes, largely due to almost negligible expression of the inward rectifier potassium current (I-K1). In the present study, we attempted to "normalize" the action potential profile of our hiPSC-CMs by inserting a voltage dependent in silico I-K1 into our hiPSC-CMs, using the dynamic clamp configuration of the patch clamp technique. Recordings were made from single hiPSC-CMs, using the perforated patch clamp technique at physiological temperature. We assessed three different models of I-K1, with different degrees of inward rectification, and systematically varied the magnitude of the inserted I-K1. Also, we modified the inserted IKi in order to assess the effects of loss- and gain-of-function mutations in the KCNJ2 gene, which encodes the Kir2.1 protein that is primarily responsible for the IKi channel in human ventricle. For our experiments, we selected spontaneously beating hiPSC-CMs, with negligible IKi as demonstrated in separate voltage clamp experiments, which were paced at 1 Hz. Upon addition of in silico IKi with a peak outward density of 4-6 pA/pF, these hiPSC-CMs showed a ventricular-like action potential morphology with a stable resting membrane potential near 80 mV and a maximum upstroke velocity >150 V/s (n = 9). Proarrhythmic action potential changes were observed upon injection of both loss-of-function and gain-of-function IKi, as associated with Andersen Tawil syndrome type 1 and short QT syndrome type 3, respectively (n = 6). We conclude that injection of in silico IKi makes the hiPSC-CM a more reliable model for investigating mechanisms underlying cardiac arrhythmia

Correction: Dissecting the Effects of Ischemia and Reperfusion on the Coronary Microcirculation in a Rat Model of Acute Myocardial Infarction.

[This corrects the article DOI: 10.1371/journal.pone.0157233.]

Area measurements of microcirculation.

<p><b>A</b> Total vessel area in nm² (including cytoplasm, lumen and nucleus). <b>B</b> Area of vessel lumen in nm². <b>C</b> Area of endothelial nuclei in nm². <b>D</b> Mean thickness of the capillary cytoplasm in nm.</p

Endothelial junctions and caveolae.

<p>Quantification of endothelial cell-cell junctions. <b>A</b> Typical TEM image of a part of two endothelial cells with cell-cell junctions (red arrows). Protruding into the lumen of the capillary (asterisk) marginal fold can be seen (blue arrow). White bar represents 100 nanometer. Magnification 17500x. <b>B</b> Quantitative analysis showing the mean number of cell-cell junctions per capillary in the infarct zones in all three groups. <b>C</b> Mean number of endothelial caveolae per capillary, as determined with transmission electron microscopy.</p