Indo-1, AM ester is membrane-permeant and thus can be loaded into cells via incubation. Because of the relatively low water solubility of the AM ester, Pluronic F-127, a mild detergent, is often used as a dispersing agent to facilitate cell loading. Indo-1/AM itself does not bind Ca2 , but it is readily hydrolyzed to Indo-1 by endogenous esterases once it enters cells.