BTC, AM CELL PERMEANT 100 UG，B6791，Invitrogen

BTC, AM is a cell-permeant coumarin benzothiazole-based Ca²⁺ indicator. It exhibits a shift in excitation maximum from about 480 nm to 400 nm upon binding Ca²⁺, which permits ratiometric measurements that are essentially independent of uneven dye loading cell thickness, photobleaching and dye leakage. BTC has high selectivity for Ca²⁺ and a K_d ~7 µM enabling quantitation of high intracellular Ca²⁺ levels^.