Heat release by isolated mouse brain mitochondria detected with diamond thermometer

TL;DR

This study unambiguously measures heat release from isolated mouse brain mitochondria using a diamond thermometer, revealing temperature increases up to 45°C during uncoupling and spontaneous bursts linked to mitochondrial activity.

Contribution

First application of a diamond thermometer to measure mitochondrial heat production, providing thermodynamic insights at the subcellular level independent of environmental factors.

Findings

Mitochondria temperature rises up to 45°C during uncoupling.

Spontaneous temperature bursts precede CCCP application.

Heat measurement is unaffected by environmental variations.

Abstract

A production of heat by mitochondria is critical for maintaining body temperature, regulating metabolic rate and preventing oxidative damage to mitochondria and cells. Up to now mitochondrion heat production was characterized only by methods based on fluorescent probes which are sensitive to environmental variations (viscosity, pH, ionic strength, quenching etc.). Herein, for the first time the heat release of isolated mitochondria was unambiguously measured by a diamond thermometer (DT) which is absolutely indifferent to external non-thermal parameters. We show that during total uncoupling of transmembrane potential by CCCP application the temperature near mitochondria rises by 4-22 {\deg}C above the ambient temperature, with an absolute maximum of 45 {\deg}C. Such a broad temperature response may be associated with the heterogeneity of the mitochondria themselves as well as their aggregations in the isolated suspension. It also revealed spontaneous temperature bursts prior to CCCP application that can reflect involvement of some mitochondria to ATP synthesis or membrane potential leaking to avoid reactive oxygen species hyperproduction. The used temperature sensor and the data obtained shed light to the thermodynamics on the subcellular level.