Chronic alcohol treatment is associated with alterations in the regulation of specific steps in the complex network of intracellular signal transduction processes that are triggered by the activation of receptors in the plasma membrane. This proposal is focused on G protein-coupled signaling processes in the liver that are mediated by phosphoinositide- specific phospholipase C and that result in the activation of protein kinase C and the elevation of cytosolic free Ca2+ concentrations ([Ca2+]i). Previous studies from our laboratory identified multiple steps that are affected by chronic ethanol intake. One of the sites affected is the inositol 1,4,5-trisphosphate (InsP3) receptor that mediates Ca2+ release from intracellular Ca2+ stores. Another site involves the feedback desensitization mechanisms that control receptor activation of phospholipase C. This feedback process appears to be involved in the development of tolerance to the effects of acute ethanol treatment, which inhibits this signaling system.
One specific aim i s devoted to the analysis of the control of the InsP3 receptor by Cab and other divalent cations. We will study the InsP3 binding to the receptor and opening of the receptor cation channel and determine ligand induced InsP3 receptor desensitization. We will also analyze the role of immunophilins and receptor phosphorylation in the changes in InsP3 receptor function induced by chronic ethanol feeding. Additionally, we will determine if chronic ethanol treatment causes changes in the endoplasmic reticular Ca2+ pump activity and the Ca2+ leak pathway and assess the contribution of mitochondrial Ca2+ fluxes to the activity of the InsP3 receptor. The second specific aim is designed to analyze the consequences of the changes in Ca2+ signaling responses for the integration of liver metabolism. We have found that changes occur in the patterns by which hormonally-induced translobular Ca2+ waves occur at low concentrations of vasopressin or other hormones. We plan to analyze the mechanistic basis of the changes in Ca2+ waves across the liver lobule and determine to what extent intercellular transfer of Ca2+ signals is a consequence of the altered cellular response after chronic ethanol feeding or involves changes in cell-cell interaction thrOugh gap junctions. We will also investigate the consequences of altered translobular Ca2+ signaling patterns for bile secretion in chronic alcoholism. Finally, we will determine if the changes in Ca2+ signaling patterns affect mitochondrial Ca2+-dependent oxidative metabolism in a heterogeneous manner across the liver lobule. Changes in hormone-induced translobular Ca2+ signaling may contribute to the liver damage associated with chronic alcohol intake.
