CALCIUM-BINDING TO BRAIN SYNAPTOSOMES - EFFECTS OF CHRONIC ETHANOL INTAKE

The effects of chronic ethanol intake (16 days) on the Ca2+ binding activity of rat brain synaptosomes were explored. Two different procedures were used for the determination of Ca2+ interactions with the synaptosomal membranes. The chelator fluorescent probe chlorotetracycline was employed for fluorescence measurements of Ca2+-membrane interaction, and the direct assay of 45Ca binding to the same preparations was used as an index of Ca2+ binding capacity at micromolar Ca2+ concentrations. Both methods gave qualitatively very similar results. Chronic ethanol treatment resulted in a significant decrease in the 45Ca binding capacity of the synaptosomal membranes which was found to be related to a decrease in the maximum number of binding sites: 11.24 nmoles·mg-1 protein for the controls as opposed to 6.10 nmoles for the ethanol-treated animals. No significant changes in the dissociation constant of this 45Ca binding to the membranes was observed. In addition, the membrane preparations from the chronically treated subjects were found to be relatively resistant to the in vitro effects of ethanol on Ca2+ interaction with the synaptosomes. Ethanol at concentrations from 5 to 100 mM caused biphasic increases of both 45Ca binding to, and CTC fluorescence of, synaptosomes from controls, though it caused minimal changes in either measure in synaptosomes from chronically ethanol-treated animals. These results are suggestive of the appearance of tolerance to the activity of ethanol at the membrane level. © 1979.