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

We describe a novel and relatively inexpensive spectrofluorescence sys tem that supplies rapidly alternating wavelengths to either a standard cuvette or an isolated perfused heart. Its use is illustrated by dete rmining changes in cytosolic intracellular Ca2+ concentration ([Ca2+]( i)) by using the Ca2+-sensitive fluorescent dye fura 2 in a rabbit hea rt preparation. The system uses two precision electromechanical shutte rs (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 o ptic 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 t he cycle are presented. Limitations of this low-cost but easily implem ented system are discussed.