Protocol to record and quantify the intracellular pH in contracting cardiomyocytes

Intracellular pH (pH_i) plays critical roles in the regulation of cardiac function. Methods and techniques for cardiac pH_i measurement have continued to evolve since early 1960s. Fluorescent microscopy is the most recently developed technique with several advantages over other techniques including higher spatial and temporal resolutions, and feasibility for contracting cell measurement. Here, we describe detailed methods for mouse cardiomyocyte isolation, and simultaneous measurement and quantification of pH_i and sarcomere length in contracting cardiomyocytes. For complete details on the use and execution of this protocol, please refer to Lyu et al. (2022).