They develop a sensor to measure intracellular temperature

They develop a sensor to measure intracellular temperature
They develop a sensor to measure intracellular temperature

Taking a person’s temperature is an easy task: a thermometer is placed under the tongue and waits for it to reach a value of around 37°C. This single measurement integrates the heat generated by the approximately 30 trillion cells in the human body. Diffusion of heat establishes body temperature, to which different cell types contribute to different degrees.

To really know how body temperature is regulated in living beings, you have to look at each cell. But even as the ability to closely observe molecular interactions has improved tremendously in the past decade, scientists have struggled to develop instruments that accurately measure the thermal properties of a cell from the inside.

A new study has just corrected this important deficiency. For the first time, thermal conductivity, that is, the speed at which they transfer heat, has been measured inside human cells. In an article published in Science  Advances, tiny diamond sensors that release heat as they measure it were used to show that it dissipates in cells much more slowly than expected. For Madoka Suzuki, a biophysicist at Osaka University and co-author of the paper, “it was very surprising to us and to others in our field.” Since the intracellular fluid is mostly water, it has always been assumed that it transmits heat like water, but it turns out that it does so about five times slower, as if it were dissipating in oil. Suzuki comments that, until now, “nobody knew about this basic property of living cells, without the assessment of which we could not model changes in cell temperature.”

According to Harvard University physicist Mikhail Lukin, who has developed sensors to explore intracellular temperature but did not work on this project, “These are fascinating results that need to be better understood. If they are confirmed, it would be quite transcendent.

These findings would help solve a great mystery about cell temperature that has baffled biologists: the existence of hyperlocalized thermal spikes. Transient differences of a few degrees Celsius have been described from one point to another within a cell, a space whose diameter ranges from 5 to 120 micrometers in humans (between the size of a dust mite’s feces and that of the mite itself). . A 2018 study even argued that mitochondria, tablet-shaped intracellular energy pumps, operate at a blistering 50°C.

The idea that cells can accommodate such large temperature gradients is surprising because, in such a tiny space, an abrupt increase in temperature should dissipate quite quickly. But the results have been convincing, says Luís Carlos, a nanoscientist at the University of Aveiro, who studies intracellular thermometry but was not involved in the new study. “I think that the experimental results of the last five years definitely point to the existence of intracellular thermal fluctuations.”

In the new work, Suzuki and his team built on Lukin’s novel technique to create a nanodiamond fluorescence sensor on a heat-releasing polymer. Local temperature changes very slightly expand the nanodiamond’s imperfections, altering its fluorescence when a laser shines on it. According to Lukin, this method is much more stable than other types of probes because diamonds are so inert.

Suzuki says that the thermal conductivity identified in the new work would explain the small 1°C spikes, but not the huge heat surge in the mitochondria. He also proposes that they may act as a hitherto unknown intracellular signaling system. For example, a pulse of heat might tell proteins to fold or unfold, to carry out certain enzymatic reactions, or to affect channels that regulate calcium concentration in muscles.

Suzuki and Lukin agree that much remains to be done to find out if these gradients really exist and how they arise. For Lukin, “This surprising problem causes us a lot of confusion and we have to solve it. The most innovative thing is that we have this new tool to answer this biological question.”

Reference: Shingo Sotoma et al. in Science Advances , vol. 7, eabd7888, 2021/2022

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