Photo-toxicity of near-infrared voltage sensitive fluorescent dyes

Abstract

The use of voltage sensitive fluorescent dyes (VSD) for noninvasive measurement of the action potential (AP) in blood perfused heart have been hindered by low interrogation depth, high absorption and auto-fluorescence of cardiac tissue. These limitations are diminished using new near infrared (NIR) VSD (di-4-ANBDQBS). Here we validated toxicity and photo-toxicity of these dyes in guinea pig and human cardiac muscle slabs. Application of NIR VSD showed no effect on cardiac muscle contraction force or relaxation. Optical action potentials closely tracked kinetics of microelectrode recorded APs in both field and electrode stimulated preparations. For phototoxicity assessment dye (50 lM) preloaded cardiac slabs were exposed to prolonged laser radiation of various power. Microelectrode AP recordings show that exposure to prolonged laser radiation (10min.; 2mW/mm2) of dye loaded tissue had no statistically significant effect on APD50 or conduction velocity, thus indicating no or weak photo-toxicity on the NIR VSD. In contrast, exposure to 5 min. laser radiation of phototoxic dyes (mitotracker deep-red) preloaded tissue caused significant reduction in APD50 (by 13%) and conduction velocity (30%). Thus, due to the low photo-toxicity, NIR VSD are well suited for in vivo cardiac imaging.