Cell permeable fluorescent indicator of intracellular Ca2+; non-fluorescent until it is hydrolyzed intracellularly and/or in the presence of Ca2+; lower binding affinity allows measurement of higher peaks of Ca2+ transients than with Fura 2.suitable as fluorescent Ca sensitive probe (after cleavage of the AM ester) Cell permeable fluorescent indicator of intracellular Ca2+; non-fluorescent until it is hydrolyzed intracellularly and/or in the presence of Ca2+; lower binding affinity allows measurement of higher peaks of Ca2+ transients than with Fura 2.