Effects of chronic ethanol treatment on mitochondrial functions damage to coupling site I

Abstract

Chronic ethanol feeding to rats produces changes in hepatic mitochondria which persist in the absence of ethanol metabolism. The integrity of isolated mitochondria is well preserved, as evidenced by unchanged activities of latent, Mg 2+- and dinitrophenol-stimulated ATPase activity, and unaltered permeability to NADH. With succinate or ascorbate as substrates, oxygen uptake by mitochondria from ethanol-fed rats was decreased compared to pair-fed controls. The decrease was comparable under state 4 or state 3 conditions, or in the presence of an uncoupler. However, with the NAD +-dependent substrates, ADP-stimulated oxygen consumption (state 3) was decreased to a greater extent than state 4 or uncoupler-stimulated oxygen consumption in mitochondria from ethanol-fed rats. This suggests that the decrease in energy-dependent oxygen consumption at site I may be superimposed upon damage to the respiratory chain. Using NAD +-dependent substrates (glutamate, α-ketoglutarate or β-hydroxybutyrate) the respiratory control ratio and the P O ratio of oxidative phosphorylation were significantly decreased in mitochondria isolated from the livers of rats fed ethanol. By contrast, when succinate or ascorbate served as the electron donor these functions were unchanged. The rate of phosphorylation is decreased 70% with the NAD +-dependent substrates because of a decreased flux of electrons, as well as a lower efficiency of oxidative phosphorylation. With succinate and ascorbate as substrates, the rate of phosphorylation is decreased 20–30%, owing to a decreased flux of electrons. These data suggest the possibility that, in addition to effects on the respiratory chain, energy-coupling site I may be damaged by ethanol feeding. Energy-dependent Ca 2+ uptake, supported by either substrate oxidation or ATP hydrolysis, was inhibited by chronic ethanol feeding. Concentrations of acetaldehyde (1–3 m m) which inhibited phosphorylation associated with the oxidation of NAD +-dependent substrates had no effect on that of succinate or ascorbate. Many of the effects of chronic ethanol feeding on mitochondrial functions are similar to those produced by acetaldehyde in vitro.