Biology subjects

Chamkha, I.

Publications and source records attributed to Chamkha, I..

2 recordsLinked to original sources

bioRxiv2022

A whole blood approach improves speed and accuracy when measuring mitochondrial respiration in avian hematocytes

Understanding mitochondrial biology and pathology is key to understanding the evolution of animal form and function. However, mitochondrial measurement often involves invasive, or even terminal, sampling, which can be difficult to reconcile in wild models or in longitudinal studies. Non-mammal vertebrates contain mitochondria in their red blood cells, which can be exploited for minimally invasive mitochondrial measurement. Several recent bird studies have measured mitochondrial function using isolated blood cells. Isolation adds time in the laboratory and might be associated with physiological complications. Inference may also be constrained on biological grounds by lack of tissue context. We developed and validated a protocol to measure mitochondrial respiration in bird whole blood. Endogenous respiration was comparable between isolated blood cells and whole blood. However, oxidative respiration was higher in whole blood, and whole blood mitochondria were better coupled and had higher maximum working capacity. Whole blood measurement was also more reproducible than measurement on isolated cells for all traits considered. Measurements were feasible over a 10-fold range of sample volumes, though both small and large volumes were associated with changes to respiratory traits. The protocol was compatible with long-term storage: after 24 h at 5 {degrees}C without agitation all respiration traits but maximum working capacity remained unchanged, the latter decreasing by 14%. Our study suggests that whole blood measurement provides faster, more reproducible, and more biologically (tissue context) and physiologically (mitochondrial integrity) relevant assessment of mitochondrial respiration. We recommend future studies to take a whole blood approach unless specific circumstances require the use of isolated blood cells.

physiology↗

bioRxiv2022

Plasticity of mitochondrial function restores fuel production during rest-phase hypothermia in a winter bird

Many animals downregulate body temperature to save energy when resting (rest-phase hypothermia). Small birds that winter at high latitude have comparatively limited capacity for hypothermia and so pay large energy costs for thermoregulation during cold nights. Available evidence suggests this process is fuelled by adenosine triphosphate (ATP)-dependent mechanisms. Most ATP is produced by oxidative phosphorylation in the mitochondria, but mitochondrial respiration can be lower during hypothermia because of the temperature-dependence of biological processes. This can create conflict between increased organismal ATP demand and a lower mitochondrial capacity to provide it. We studied this in blood cell mitochondria of wild great tits (Parus major) by simulating rest-phase hypothermia via a 6{degrees}C reduction in assay temperature in vitro. The birds had spent the night preceding the experiment in thermoneutrality or in temperatures representing mild or very cold winter nights. Night temperature did not affect mitochondrial respiration. Across treatments, endogenous respiration was 14% lower in hypothermia. This did not reflect general thermal suppression because phosphorylating respiration was unaffected by thermal state. Instead, hypothermia was associated with a threefold reduction of leak respiration, from 17% in normothermia to 4% in hypothermia. Thus, coupling of total respiration to ATP production was 96% in hypothermia, compared to 83% in normothermia. Our study shows that thermal insensitivity of phosphorylation combined with short-term plasticity of leak respiration may safeguard ATP production when endogenous respiration is suppressed. This casts new light on the process by which small birds endure harsh winter cold and warrants future tests across tissues in vivo.

physiology↗