An increasing amount of direct and indirect evidence indicates that ethanol markedly decreases both cellular and plasma Mg2+ content through mechanisms which are poorly understood. The goal of the present project is to characterize, at the cellular and subcellular level, how the acute and chronic administration of ethanol impairs Mg2+ homeostasis in liver cells, and possibly cardiac myocytes, to induce a decrease in total cellular Mg2+. This decrease is the result of a prolonged and massive intake of ethanol, and is deleterious to tissues. Hence, the characterization of the mechanisms responsible for this depletion would permit to operate preventively, to reduce the insurgence of alcohol-related pathologies such as cirrhosis and alcoholic cardiomyopathy. The preliminary data reported here indicate that the acute perfusion of livers with varying doses of ethanol induces a detectable and selective loss of Mg2+ from liver cells through a specific Mg2+ extrusion mechanism, tentatively identifiable with a Na+/Mg2+ exchanger. The Mg2+ extrusion is prevented by the alcohol dehydrogenase inhibitor 4-methyl-pyrazole, by amiloride, or by the removal of external Na+. There are four principal aims: 1.) To investigate whether, by mobilizing Mg2+ from different tissues, the acute administration of ethanol to anesthetized rats induces a rapid and transient increase in serum Mg2+ level. 2.) To determine the mechanisms responsible for the specific extrusion of Mg2+ across the cell plasma membrane following acute administration of ethanol. 3.) To investigate whether ethanol-induced Mg2+ extrusion affects only the cytosolic compartment or results in a major redistribution of Mg2+ among cytosol and intracellular compartments, and 4.) To determine to what extent Mg2+ transport and regulatory mechanisms are affected following chronic ethanol treatment.
These Aims will be investigated in perfused livers and hearts, isolated cells and purified subcellular organelles obtained from organs acutely treated with ethanol, or isolated from ethanol-fed rats. The results so obtained will provide a critical and necessary background of knowledge for future more mechanistic studies aimed at correlating Mg2+ deficiency with impairment of body or organ functions.
