Figure 1

Schematic drawing of experimental setup. The mouse heart is perfused in Langendorff mode with warm oxygenated Tyrode’s solution delivered at a constant pressure through heat-jacketed tubing ( 3). The heart is immersed in a re-circulated bath containing warm oxygenated Tyrode’s solution ( 4) along with a cradle for two volume-conducted EKG electrodes and a platinum pacing electrode ( 2). Illumination is provided at 380 and 340 nm by a high speed switching light source ( 6). Emitted fluorescence passes through a 510 nm band-pass filter and is recorded on a high-speed CCD camera ( 1). Timing for the illumination and the camera are provided by a custom computer program ( 7); the pacing electrode and EKG leads ( 5) interface with the computer through a PowerLab system.