Ethanol potentiation of glycine receptors expressed in Xenopus oocytes antagonized by increased atmospheric pressure.
BACKGROUND
Behavioral and biochemical studies indicate that exposure to 12 times normal atmospheric pressure (12 ATA) of helium-oxygen gas (heliox) is a direct, selective ethanol antagonist. The current study begins to test the hypothesis that ethanol acts by a common mechanism on ligand-gated ion channels by expanding previous hyperbaric investigations on gamma-aminobutyric acid type A (GABA(A)) receptors (GABA(A)Rs) at the biochemical level to alpha(1)glycine (GlyRs) expressed in Xenopus oocytes.


METHODS
Oocytes expressing wild-type alpha(1) homomeric GlyRs were voltage-clamped (-70 mV) and tested in the presence of glycine (EC(2)) +/- ethanol (50-200 mM) under 1 ATA control and 3 to 12 ATA heliox conditions. Glycine concentration response curves, strychnine/glycine interactions, and zinc (Zn2+) modulation of GlyR function was also tested.


RESULTS
Pressure reversibly antagonized the action of ethanol. The degree of antagonism increased as pressure increased. Pressure did not significantly alter the effects of glycine, strychnine, or Zn2+, indicating that ethanol antagonism by pressure cannot be attributed to alterations by pressure of normal GlyR function. The antagonism did not reflect tolerance to ethanol, receptor desensitization, or receptor rundown.


CONCLUSIONS
This is the first use of hyperbarics to investigate the mechanism of action of ethanol in recombinant receptors. The findings indicate that pressure directly and selectively antagonizes ethanol potentiation of alpha(1)GlyR function in a reversible and concentration- and pressure-dependent manner. The sensitivity of ethanol potentiation of GlyR function to pressure antagonism indicates that ethanol acts by a common, pressure-antagonism-sensitive mechanism in GlyRs and GABA(A)Rs. The findings also support the hypothesis that ethanol potentiation of GlyR function plays a role in mediating the sedative-hypnotic effects of ethanol.
Davies
Daryl L
DL
Alcohol and Brain Research Laboratory, Department of Molecular Pharmacology and Toxicology, School of Pharmacy, University of Southern California, Los Angeles, CA 90033, USA. ddavies@usc.edu
Trudell
James R
JR
Mihic
S John
SJ
Crawford
Daniel K
DK
Alkana
Ronald L
RL
D000494:Allosteric Regulation; D000818:Animals; D001274:Atmospheric Pressure; D004347:Drug Interactions; D000431:Ethanol / Q000494:pharmacology*; D005260:Female; D015870:Gene Expression; D005998:Glycine / Q000494:pharmacology; D006801:Humans; D009865:Oocytes / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D018009:Receptors, Glycine / Q000037:antagonists & inhibitors* / Q000187:drug effects* / Q000235:genetics; D011994:Recombinant Proteins; D013331:Strychnine / Q000494:pharmacology; D014162:Transfection; D014982:Xenopus laevis; D015032:Zinc / Q000494:pharmacology
D018009:Receptors, Glycine; D011994:Recombinant Proteins; D000431:Ethanol; D013331:Strychnine; D015032:Zinc; D005998:Glycine