NPs-induced changes in cellular electrophysiology. A. Representative action potential (AP) waveforms recorded from control (CTRL, black line) and TiO2-NP (NPC, red line) cardiomyocytes at the physiological driving rate of rat heart (5 Hz). B–E. Graphs of action potential duration (APD) measured at − 20 mV (APD20) and − 60 mV (APD60), beat- to- beat variability of APD60 (CVAPD60), AP upstroke (UPS) and membrane capacitance (Cm). In all graphs, CTRL is given by white columns, and NPC by the red columns (n = 37 NPC and n = 49 CTRL). *, p < 0.05 vs. CTRL. F. APs simulated with the Pandit model, without (black trace, CTRL) and with (red trace, NPC) a simulated 1.5 nS constant potassium leakage.