Assessing mitochondrial quality in nontraditional animal models

Studying mitochondrial respiratory function is critical to understanding the plasticity of cellular energetics. Mitochondrial respiratory function is usually studied ex vivo and requires isolation of high-quality mitochondrial preparations. However, mitochondria are usually damaged by this process, and the degree of damage is typically assessed by measuring respiratory control ratios (RCRs) and the change in respiration rate mediated by exogenous cytochrome C addition to isolated mitochondrial preparations. The standard thresholds in the field for determining whether isolated mitochondria are “acceptable” are based on studies in common laboratory rodents and are entirely arbitrary. However, zoologists are increasingly employing nonstandard animal models in the study of mitochondrial respiratory function across a wide variety of fields and there is growing evidence that the canonical thresholds of acceptable RCRs and the cytochrome C response that have been used to identify healthy mitochondrial preparations may not be useful in other species. In this commentary, we discuss the limitations of using RCRs and cytochrome C-mediated changes in mitochondrial respiration in the study of nontraditional laboratory species and propose alternative means of evaluating mitochondrial integrity that may permit more accurate assessment of the quality of mitochondria isolated, and thus better support comparison of data across species and studies.