The enhancement of L-glutamic acid binding activity of brain synaptic membranes by low concentrations of ethanol (<50 mM) and the decrease in binding at high concentrations (>100 mM) was not due to a direct action by ethanol on the glutamate binding protein. Biphasis effects of ethanol on membrane protein complexes such as the glutamate binding sites might be the result of biphasic changes in membrane lipid organization. Low ethanol concentrations (0.1-4.0 mM) were shown to decrease fatty acid chain motion detected by the EPR probe 5-doxyl stearic acid, whereas high concentrations (>400 mM) increased lipid motion in egg phosphatidylcholine liposomes. The function of the L-glutamate receptor-ion channel complex in the presence of ethanol was also determined by measuring the changes in thiocyanate (SCN-) influx brought about by L-glutamate or ethanol. A low concentration of ethanol (9.4 mM) diminished the L-glutamate-induced depolarization of synaptic membranes, while a high concetration (93.7 mM) increased the passive SCN- influx and produced a transient overshoot in glutamate-stimulated SCN- flux.
Bibliographical noteFunding Information:
The authors wish to thank Ms. Kathy Wright for her excellent assistance in the typing of this manuscript. This research was supported by a grant from NIAAA, AA 04732, by a research award DAAG 29-79-C-0156 from the United States Army Research Office, and by funds from Biomedical Research Support Grant RR 5606. The authors acknowledge the support provided by the Center for Biomedical Research-The University of Kansas.
- Glutamate receptors
- Membrane lipids
- Membrane structure
- Synaptic membranes