Intracellular Calcium Flux in iPSC Cardiomyocytes

Intracellular calcium flux in iPSC cardiomyocytes exposed to the test solutions for 120 min was measured using FLIPR tetra (Molecular Devices) instrument using the EarlyTox Cardiotoxicity Kit as described previously.^{9 (link), 12 (link)} Cardiomyocytes were incubated for 2 hours at 37ºC following the addition of one volume of pre-equilibrated calcium-dye reagent. Prior to exposure of iPSC cardiomyocytes to test solutions, baseline calcium flux measurements were recorded at 515–575 nm following excitation at 470–495 nm and at a frequency of 8 hz for 100 seconds. The internal instrument temperature was regulated at 37ºC. Cells were then simultaneously exposed to test solutions using the internal fluidics handling system. 120 min post-exposure, the beating of iPSC cardiomyocytes was monitored as specified above. Between measurements, cells were incubated under cell culture conditions at 37°C and 5% CO₂. Recorded data were processed in Screenworks 4.0 software (Molecular Devices LLC., Sunnyvale, CA) and statistical parameters were exported as Microsoft Excel files for concentration-response assessment.