FURA-2 DETERMINATION OF [CA2+](I) IN ISOLATED-PERFUSED HEART USING R-WAVE-GATED ELECTROMECHANICAL SHUTTERS

We describe a novel and relatively inexpensive spectrofluorescence system that supplies rapidly alternating wavelengths to either a standard cuvette or an isolated perfused heart. Its use is illustrated by determining changes in cytosolic intracellular Ca2+ concentration ([Ca2+](i)) by using the Ca2+-sensitive fluorescent dye fura 2 in a rabbit heart preparation. The system uses two precision electromechanical shutters (capable of gating with respect to the electrocardiographic R wave for signal averaging) allowing alternate fura 2 excitation wavelengths (340 and 380 nm) without moving optical components and uses a fiber optic for conducting excitation and collecting epifluorescence. Sample recordings tracing the [Ca2+](i) transient in an entire cardiac cycle and in capturing specific isolated regions (diastole and systole) of the cycle are presented. Limitations of this low-cost but easily implemented system are discussed.