Biochemical and Morphological Aspects of Mitochondrial Swelling in Ammonia Toxicity 1

Abstract

Summary

Molecular aspects of ammonia intoxication were studied with rat liver mitochondria swelling spontaneously in buffered isotonic sucrose solution containing ⁴⁵C label. Results were compared with electron microscopic study of livers of ammonia intoxicated rats.

Small concentrations of NH₄Cl (4 and 6 mM) added to the swelling media markedly decreased the labeling of mitochondria. This decreased labeling was found to be due to increased efflux of the label. Ammonia also caused increased loss of intramitochondrial magnesium and phosphate.

Ammonium, phosphate and magnesium variably and increasingly reduced ⁴⁵Ca labeling of swelling mitochondria, but when all three ions were present in the medium, the reduction in labeling was not additive. A crystalline material was isolated from the supernatant fraction after high speed centrifugal separation of the mitochondria previously swelling in the medium containing added Mg, PO₄ and NH₄ ions. This material was identified as magnesium ammonium phosphate by infrared spectrography.

Electron micrographs of liver of the hyperammonemic rat revealed radical changes to fine structure of the liver cell. Mitochondria were swollen to many times normal size, with considerable loss of mitochondrial matrix. Disorganization of the endoplasmic reticulum was also apparent.

The effect of ammonia on respiring mitochondria may not only be substrate and cofactor depletion but may also be due to morphological changes to mitochondrial membrane structure through magnesium loss, although the mechanism by which this occurs would be similar.