INTRALOBULAR METABOLIC HETEROGENEITY AND LIVER INJURY

The early signs of liver injury due to ethanol (e.g., fatty degeneration) occur in the pericentral region of the liver lobule. The biochemical and cellular mechanisms underlying this intralobular zonation of ethanol-induced liver injury are largely unknown. To investigate this problem, the applicant developed the micro-light guide and the mini-oxygen electrode to measure the oxygen gradients across the periportal and pericentral regions of the liver lobule. Research carried out with the isolated, hemoglobin-free perfused rat liver produced evidence that the treatment of the rat with ethanol increased the rate of oxygen uptake by pericentral cells without affecting the respiratory activity of periportal cells. In the present grant proposal, a new hypothesis concerning the mechanism of ethanol-induced pericentral liver injury is formulated on the basis of this observation, and critical experiments designed to test this hypothesis are proposed. According to this hypothesis, ethanol selectively uncouple mitochondria in the pericentral region by causing an influx of Ca+2 and Na+ into the cytosol secondary to plasma membrane depolarization resulting from ethanol-induced inhibition of glycolysis. Following the measurements of the periportal and pericentral oxygen gradients, the perfused liver will be rapidly frozen and thin-sectioned in a cryostat. Quantitative histochemical techniques will be applied to the air-dried thin sections of the liver to measure the intracellular phosphate potential, (ATP)/(ADP)(Pi), the (NADH) (NAD+) ratio, and the lipid content of hepatocytes in the periportal and pericentral regions of the liver lobule. The micro-light guide and fluorescence microscopy will be employed to measure the plasma membrane and mitochondrial inner membrane potentials using voltage-sensitive dyes and lipid soluble organic ions. To investigate the effects of chronic ethanol treatment on the immunological properties of periportal and pericentral cells, methods will be developed to raise monoclonal antibodies to these cells and their binding characteristics will be studied in the perfused rat liver. The proposed studies will contribute to our understanding of the possible roles of metabolic and "immunological" zonations of the hepatic acinus in the basic physiology and pathophysiology of the liver.