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Temperatures for respirometry

From Bioblast

Experimental temperature

Ideally, experiments on biological systems should be conducted at the temperature at which the system usually operates, the so-called physiological temperature, which is for most tissues, cells and mitochondria of mammalian origin 37°C.
This temperature should be regularly used as an experimental temperature for the determination of mitochondrial respiratory activity in HRR, no matter whether working with biopsies, cultured cells or isolated mitochondria.
When measuring in an appropriate medium (protecting and stabilizing mitochondrial function) stability is preserved even in isolated mitochondria.

Practically, measuring respiration at 37°C has the disadvantage of requiring a potent temperature control unit to minimize temperature fluctuations. Further, at 37°C a relatively rapid exhaustion of medium oxygen content may be observed in closed-type respirometers. This necessitates that either the amount of biological sample is reduced, at the expense of a reduced signal-to-noise ratio of the measurement, or that measures are taken that allow for repeated re-oxygenation of the measuring chamber (Fasching 2016 MiPNet14.13). Therefore, the temperature used in many older studies was close to the poorly-defined room temperature, somewhere between 20°C and 25°C. While such protocols are still in use nowadays and evidence has been put forward that the temperature effect may not be as pronounced as expected (Perry et al 2013), it is arguably unphysiological and accepts a certain level of uncertainty regarding the temperature effect.
It should be noted here that it is now widely recognized that body temperature even of so-called homeotherms may show considerable variations related to activity levels and age (Weinert and Waterhouse 2007; Weinert 2010). Whether mitochondria behave energetically different in accordance with such alterations of temperature and metabolic state remains yet to be detected. Furthermore, an increasing number of mammals and birds are now known to actually be heterothermic, i.e. to change body temperature in a diurnal or season-dependent manner to a considerable extent (Grigg et al 2004). In these animals there is clear evidence that mitochondrial metabolism is altered according to temperature and metabolic state (Staples et al 2008; Kutschke et al 2013), but even there this cannot be generalized (Grimpo et al 2013).
For respirometric samples from birds, also regarded as homeothermic animals, the same principles apply as for mammals, whereas for the “classical” heterothermic study objects, i.e. vertebrates excluding mammals and birds and for invertebrates, there is apparently no general rule other than the plausible assumption that it may be wise to make measurements at a temperature well within the typical range experienced by the organism.

Further information

» Publications about temperature, hypothermia, hyperthermia
» Peltier temperature control of O2k