Modulation of cardiomyocyte contractility and action potentials with chemogenetic chloride currents

Transient perturbation of electrical activity is regularly used in neuroscience to study the impact of specific neuronal cell populations on brain function. Similarly, cardiomyocyte physiology can be controlled by the activation of artificially expressed ion channels. Pharmacologically selective actuator modules (PSAMs) are engineered ion channels that can be activated with small molecular substances and have been used to modulate neuronal activity. We aimed to use the “inhibitory” PSAMs, i) PSAML141F,Y115F-GlyR (PSAM-GlyR) and ii) PSAML131G,Q139L,Y217F (ultrapotent PSAM4-GlyR) which consist of modified α7 nicotinergic acetylcholine receptor ligand binding domains and the chloride-selective ion pore domain of the glycine receptor, to study chloride currents in cardiomyocytes and modulate cardiomyocyte physiology. We employed CRISPR/Cas9 to integrate PSAM-GlyR and PSAM4-GlyR in induced pluripotent stem cells, differentiated cardiomyocytes and generated engineered heart tissue. PSAM-GlyR and PSAM4-GlyR activation allowed to titrate chloride currents in a reversible manner. Using video optical force recordings, sharp microelectrode action potential recordings and patch-clamp technique we found that chloride currents modulate action potential characteristics. Patch clamp recordings showed that channel activation resulted in chloride-driven inward currents that depolarized the cell. In engineered heart tissue this resulted in an inhibition of contractility that was fully reversible after wash-out.