High-speed Intracellular Temperature Mapping Reveals the Existence of Non-Conductive Dissipation of Energy by Heating

Abstract

AbstractRecently, intracellular thermometry has revealed temperature variations within cells. Although the biological significance of intracellular temperature change is recognized, the physical principles of intracellular temperature change remain a mystery. Here, we investigate intracellular heat transfer through intracellular temperature mapping using a fluorescent polymeric thermometer and high-speed fluorescence lifetime imaging microscopy. Through infrared laser irradiation assisted heating, we track changes in temperature distribution to examine the mechanism of intracellular heat dissipation in relation to heat conduction. Continuous heating provokes the significantly slower (second order) relaxation of averaged temperature of single cells compared to liposomes of comparable size, and is affected by intracellular structures and molecules. Furthermore, we reveal the existence of intracellular temperature relaxation independent of heat conduction. Our results may explain the mechanisms of temperature variation in cells that are unresolved based on our current understandings, providing the first step toward unraveling intracellular thermodynamics under non-equilibrium conditions.