Validity of respiration measures in isolated mitochondria?

[asimov42]

I've recently read a couple of papers on exercise and mitochondria (see e.g., http://www.sciencedirect.com/science/article/pii/S0891584907008349), in which state 4 and state 3 respiration rates and ROS production are assessed in vitro after exercise has been performed (i.e., rat heart mitochondria are isolated).

My question: given that it takes 1 hr. for the mitochondria to be removed from the animal and isolated, that additional (saturating) substrate is added before respiration parameters are measured, and that the medium is saturated to the ambient oxygen concentration (much higher than in vivo), is this type of experiment really valid to assess mitochondrial function in vivo in active animals? Opinions and/or pointers to resources that clarify how useful these measurements are would be helpful.

Thanks!
J.

 

[Zefram]

Smith

Dear J. Smith,

Thank you for bringing up an important question regarding the validity of using in vitro experiments to assess mitochondrial function in vivo. While these types of experiments can provide valuable insights into the biochemical processes of mitochondria, it is important to consider the limitations of these methods.

Firstly, isolating mitochondria from tissue and then subjecting them to different conditions in vitro may not accurately reflect the in vivo environment. Mitochondria function in a complex and dynamic manner within the cell, and their interactions with other cellular components can greatly influence their function. Therefore, the results obtained in isolated mitochondria may not be representative of their function in the intact organism.

Furthermore, as you mentioned, the addition of additional substrates and the use of a saturated oxygen environment may not accurately reflect the conditions in vivo. These factors can greatly influence the respiration rates and ROS production of mitochondria, and may not accurately reflect their function in a physiological setting.

There is also the issue of time delay between the isolation of mitochondria and the measurement of their function. As mitochondria are constantly undergoing changes and adaptations, the results obtained from isolated mitochondria may not accurately reflect their function at the time of isolation.

In conclusion, while in vitro experiments can provide valuable information about mitochondrial function, they should be interpreted with caution and their limitations should be taken into consideration. It is important to also supplement these experiments with in vivo studies to fully understand the complex role of mitochondria in the body.

I hope this helps answer your question. For further resources on this topic, I suggest looking into reviews or textbooks on mitochondrial biology and metabolism.