Factors affecting actions of ethanol on GABA-activated chloride channels.
Effects of ethanol in vitro on membrane vesicles (microsacs prepared from mouse cerebral cortex) were evaluated by monitoring 36Cl- influx. Different assay parameters were tested to determine increased or decreased action of ethanol on GABA-activated chloride channels. The ability of 30 mM ethanol to augment 36Cl- flux was seen at 0 degrees C, in the absence of GABA ("direct" action of ethanol), and at 34 degrees C in the presence of GABA, using two different assay procedures. Picrotoxin blocked the direct effects of ethanol (at 0 degrees C) suggesting GABAa involvement. Endogenous GABA in the medium surrounding the microsacs was assayed at different temperatures both in the presence and absence of GABA and ethanol. The direct effect of ethanol did not appear to involve the action of endogenous GABA. In addition to temperature effects on the assay, time of membrane storage also influenced ethanol action. Microsacs stored on ice for 2 hours or more lost their ability to respond to ethanol but not to GABA, pentobarbital or flunitrazepam. When these drugs were tested on membranes from mice that had been sacrificed by cervical dislocation as opposed to decapitation, ethanol did not augment GABA-stimulated chloride flux. The method of sacrifice did not influence the response to GABA, pentobarbital or flunitrazepam.
Research Service, VA Medical Center, Denver, CO.
S J
SJ
McQuilkin
R A
RA
Harris
D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D003080:Cold Temperature; D000431:Ethanol / Q000633:toxicity*; D005260:Female; D005445:Flunitrazepam / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects*; D051379:Mice; D010424:Pentobarbital / Q000494:pharmacology; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000032:analysis / Q000494:pharmacology*
D002712:Chlorides; D007473:Ion Channels; D000431:Ethanol; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam; D010424:Pentobarbital