Effect of monensin on the morphology of mitochondria in rodent and equine striated muscle.

This research studied the impact of monensin, an antibiotic, on the morphology of mitochondria in the muscle cells of rodents and horses. The study revealed that exposure to monensin led to noticeable changes in the muscle cells’ mitochondria, characterized by loss of matrix substance and swelling, potentially indicating monensin poisoning.

Methodology and Observations

• Researchers examined heart, diaphragm, and rear limb muscle from rats and ponies that had been treated with monensin using light and electron microscopy. These techniques allowed for the visualization and study of the morphological alterations within the mitochondria.
• In both species, certain muscle cells showed ‘mitochondrial aberrations,’ essentially changes in the usual structure and function of mitochondria. These changes were characterized by vacuolization (loss of matrix substance), often coupled with swelling of the structure. These vacuolated mitochondria were almost completely devoid of matrix substance but retained the basic form of the mitochondrial cristae.

Species-Specific Findings

• In ponies, most of these vacuolated mitochondria were found in heart muscle, with a lesser number observed in the diaphragm. In contrast, rats showed the most vacuolated mitochondria in their diaphragm, with fewer found in the rear limb and heart muscles.
• Within the rat diaphragm, researchers differentiated between red and white muscle fibers based on their size and mitochondrial content. They found a roughly equal number of vacuolated mitochondria in each muscle fiber type when the total number of vacuolated mitochondria was small. However, when large numbers of mitochondria were vacuolated, the majority were seen in white muscle fibers.

Implications for Monensin Poisoning

• The researchers suggest that the form and distribution of vacuolated mitochondria could serve as indicators of monensin poisoning, given their distinct and observable changes.
• It’s also suggested that mitochondrial vacuolation might be a secondary effect of monensin toxicity, as this change does not take place in cultured cells (both plant and animal) or in root plants directly exposed to monensin. This implies that the observed effects in muscle mitochondria might be a result of the organism’s response to monensin, rather than a direct effect of the antibiotic.