The Use of Ratiometric Fluorescence Measurements of the Voltage Sensitive Dye Di-4-ANEPPS to Examine Action Potential Characteristics and Drug Effects on Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes. - Hortigon-Vinagre MP; Zamora V; Burton FL; Green J; Gintant GA; Smith GL (Toxicological sciences : an official journal of the Society of Toxicology, 2016)