(52) EFFECT OF CHRONIC ALCOHOLISM ON FUNCTIONAL BLOCKS OF THE OXIDATIVE PHOSPHORYLATION SYSTEM IN HEART AND LIVER MITOCHONDRIA

A. Marcinkeviciute (1,2), V. Mildaziene (1,2), B.N. Kholodenko (1), J.B. Hoek (1)
(1) Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, PA, USA
(2) Institute for Biomedical Research, Kaunas Medical Academy, Kaunas, Lithuania

Long-term alcohol consumption affects mitochondrial energy metabolism in different tissues, but the functional consequences of these effects remain poorly characterized. We analyzed the effect of chronic alcohol consumption on liver and heart mitochondria from control and ethanol-fed rats after 2 months, 11 months and 18 months of ethanol diet. We studied separate functional blocks of oxidative phosphorylation system, the respiratory subsystem, phosphorylation subsystem and proton leak by titration with inhibitors of phosphorylation and oxidation, respectively, and measuring O2 uptake rates and membrane potential.

Although liver mitochondria from ethanol-fed (2 months) rats respiring in State 3 on succinate or glutamate + malate exhibited lower respiration rates, membrane potentials (DY) did not differ significantly from the control preparation. This suggests, that in State 3 both electron transport and phosphorylation were inhibited by ethanol feeding to an almost equal degree. Longer term (18 months) of ethanol diet increased the inhibitory effect of ethanol on the rate of phosphorylation in liver mitochondria but the respiratory subsystem in liver mitochondria was inhibited by ethanol consumption to an almost equal degree after 2 and 18 months of ethanol diet both for succinate and for glutamate + malate oxidation. However, the inhibition of glutamate + malate oxidation was stronger than for succinate, suggesting additional damage to complex I. After 2 months of ethanol diet there was no change in the dependence of proton leak on DY in liver mitochondria. However, 18 months of ethanol consumption increased the slope of this dependence in both heart and liver mitochondria, compared with pair-fed control animals.

In heart mitochondria from ethanol-fed animals (11 and 18 months on diet) the respiratory subsystem was not suppressed, but even activated over the entire range of DY between State 3 and State 4. Respiration rates in State 3 (succinate or pyruvate + malate as substrates) were significantly higher than in control mitochondria both after 11 and 18 months on ethanol diet. Moreover this difference in respiration rate persisted at all values of DY between States 3 and 4, and not only near State 3 as in liver mitochondria. At the same time, differences in phosphorylation activity due to prolonged alcohol treatment in heart mitochondria were modest.

The differential effect of alcohol on certain blocks of oxidative phosphorylation in heart and liver mitochondria suggest the existence of a variety of compensatory mechanisms involved in the adaptation to alcohol in these two tissues.