Human Engineered Heart Tissue Models for Pharmacological Studies-Inhibition of Small-Conductance Ca ²⁺ -activated K ⁺ (K _Ca 2) channel

Atrial fibrillation (AF) is a common cardiac arrhythmia increasing stroke risk. Current treatments show limited effectiveness and can cause serious side effects. At the moment there is a lack of well-established human models recapitulating complex cardiac microenvironment for studying potential AF therapies. To address the limitations of existing models we developed 3D in vitro human Engineered Heart Tissue (EHT) model using atrial and ventricular human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) with either human atrial fibroblasts (HAF) or human ventricular fibroblasts (HVF).These chamber-specific EHTs exhibit differences in gene expression, ion channels and physiological responses, enabling studying Frank-Starling mechanisms and Ca ²⁺ response. Using K _Ca 2 channel inhibitor AP14145, we observed increased contraction force and prolonged relaxation time, suggesting negative modulation of K _Ca 2.2/K _Ca 2.3 channels and increased atrial-effective refractory period (AERP). The EHT model provides a valuable platform for examining K _Ca 2 channel inhibitors impact and evaluating chamber-specific drug effects in controlled in vitro settings.