Rhodamine 800 as a near-infrared fluorescent deposition flow tracer in rodent hearts

We investigated the use of a near-infrared (NIR) fluorescent dye, Rhodamine 800 (Rhod800, lambda(exc) = 693 nm, lambda(em) > 720 nm) as a flow-dependent molecular tracer for NIR spectroscopy and high-resolution cardiac imaging. Rhod800 accumulates in isolated mitochondria in proportion to the mitochondrial membrane potential (Delta Psi). However, in the intact myocardium, Rhod800 binding is Delta Psi-independent. Rat hearts were perfused in a Langendorff mode with Krebs-Henseleit buffer containing 45-nM Rhod800 at normal (100%), increased (150%), or reduced (50%) baseline coronary flow (CF) per gram, for 30 to 60 min. In a different group of hearts, the left anterior descending artery (LAD) was occluded prior to Rhod800 infusion to create a flow deficit area. Rhod800 deposition was analyzed by: 1. absorbance spectroscopy kinetics in the Rhod800-perfused hearts, 2. Rhod800 absorbance and fluorescence imaging in the short-axis heart slices, and 3. dynamic epicardial/subepicardial fluorescence imaging of Rhod800 in KCl-arrested hearts, with a spatial resolution of similar to 200 mu m. Rhod800 deposition was proportional to the perfusate volume (CF and perfusion time) and there was no Rhod800 loss during the washout period. In the LAD-ligated hearts, Rhod800 fluorescence was missing from the no-flow, LAD-dependent endocardial and epicardial/subepicardial area. We concluded that Rhod800 can be used as a deposition flow tracer for dynamic cardiac imaging. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3583581]