Modification of glycoprotein residues as Ca2+ receptor sites after chronic ethanol exposure

Previous studies have demonstrated that chronic low-dose administration of ethanol in the drinking fluid of rats produces an increase in content of calcium on synaptic membranes. In the present study, ethanol was studied in vitro and in vivo for its effects on Ca2+ binding to a high affinity receptor site on synaptic membranes. Ethanol (1-50 micrometer) significantly inhibits the binding of Ca2+ in non-competitive fashion, together with inhibiton of a cooperative mechanism for Ca2+ binding. Ruthenium red and neuraminidase were used to probe surface glycoprotein sites as receptors for Ca2+. Use of these probes together with ethanol in vitro or in vivo suggests that increases in Ca2+ receptor sites after chronic ethanol exposure are related to an increase in sialic acid exposure, possibly as a result of conformational changes in membrane protein. These findings are consistent with the hypothesis that chronic low-dose exposure to ethanol causes changes in proteins of synaptic membranes, which may in turn regulate the cellular adaptation to ethanol.