Required G1 to Suppress Automaticity of iPSC-CMs Depends Strongly on I1 Model Structure

Abstract

Human-induced pluripotent stem cells derived cardiomyocytes (hiPSC-CMs) are a virtually endless source of human cardiomyocytes that may become a great tool for safety pharmacology; however, their electrical phenotype is immature: they show spontaneous action potentials (APs) and an unstable and depolarized resting membrane potential (RMP) because of lack of I_K1. Such immaturity hampers their application in assessing drug safety. The electronic overexpression of I_K1 (e.g., through the dynamic clamp (DC) technique) is an option to overcome this deficit. In this computational study, we aim to estimate how much I_K1 is needed to bring hiPSC-CMs to a stable and hyperpolarized RMP and which mathematical description of I_K1 is most suitable for DC experiments. We compared five mature I_K1 formulations (Bett, Dhamoon, Ishihara, O'Hara-Rudy, and ten Tusscher) with the native one (Paci), evaluating the main properties (outward peak, degree of rectification), and we quantified their effects on AP features (RMP, V˙_max, APD₅₀, APD₉₀ (AP duration at 50 and 90% of repolarization), and APD₅₀/APD₉₀) after including them in the hiPSC-CM mathematical model by Paci. Then, we automatically identified the critical conductance for I_K1 ( G_{K1, critical}), the minimally required amount of I_K1 suppressing spontaneous activity. Preconditioning the cell model with depolarizing/hyperpolarizing prepulses allowed us to highlight time dependency of the I_K1 formulations. Simulations showed that inclusion of mature I_K1 formulations resulted in hyperpolarized RMP and higher V˙_max, and observed G_{K1, critical} and the effect on AP duration strongly depended on I_K1 formulation. Finally, the Ishihara I_K1 led to shorter (-16.3%) and prolonged (+6.5%) APD₉₀ in response to hyperpolarizing and depolarizing prepulses, respectively, whereas other models showed negligible effects. Fine-tuning of G_K1 is an important step in DC experiments. Our computational work proposes a procedure to automatically identify how much I_K1 current is required to inject to stop the spontaneous activity and suggests the use of the Ishihara I_K1 model to perform DC experiments in hiPSC-CMs.