Measurement of Temperature Change in Single Hela Cells with Thermosensitive Polymers

Abstract

Temperature is one of the most important parameters for living cells. Relationship between temperature and the processes in cells, i.e. effects of temperature on the cellular activities, has been studied for many years. However, there have been few studies focusing on the intracellular temperature of single living cells, because there have been few appropriate methods. In this study, we have developed a new method to measure a local temperature change inside single cells with molecular thermometers. We used thermosensitive fluorescent polymer, poly(DBD-AE-co-NNPAM-co-NIPAM) as a molecular thermometer. The fluorescence intensity of the polymer in cytosol sharply increases more than 10-fold by 6-7 °C increase around the transition temperature. We first tried to detect the thermogenesis in single HeLa cells induced by ionomycin, which was previously studied with using a micro thermometer made of a glass capillary (Suzuki, M. et al., Biophys. J. 92, L46-L48, 2007). When ionomycin was added to extracellular solution, the fluorescence intensity of polymers inside HeLa cells increased. However, the polymers also responded to DMSO, in which ionomycin was dissolved, so that this property made it difficult to accurately determine the temperature change. Therefore, we have developed another method composed of a thermosensitive sheet, which complements the measurement with polymers. As a result, we found that the temperature increase occurred due to ionomycin treatment.