A chemical procedure for loading the calcium indicator acquorin into mammalian working myocardium

The bioluminescent calcium indicator aequorin was successfully loaded into mammalian working myocardium of ferrets by a chemical procedure which makes the cells reversibly hyperpermeable through exposure to Ethylenebis-( oxyethylenenitrilo ) tetraacetic acid (EGTA). After undergoing the loading procedure, developed tension at Lmax was 103 +/- 26% of the control, which indicates that the muscles regained normal function. The configurations of the aequorin signals (i.e., calcium transients) and their responses to drugs were the same as reported after microinjection of aequorin. The peak of the Ca++ transient determined by the method of fractional luminescence at 3s intervals of stimulation, 2.5mM [Ca++]o, 22.5 degrees C was 1.1 microM; this value is similar to that reported for microinjection. These results indicate that the chemical loading procedure is a useful alternative to microinjection for loading aequorin into mammalian working myocardium.