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Vol. 285, Issue 2, 680-686, May 1998
-Aminobutyric AcidA Receptor
Activity by
-Chloralose1
Department of Physiology, University of Oklahoma Health Sciences
Center, Oklahoma City, Oklahoma
-Chloralose is widely used as an anesthetic in the laboratory due to
its minimal effects on autonomic and cardiovascular systems, yet little
is known about its mechanism of action. We examined the effects of
-chloralose on
-aminobutyric acid type A (GABAA)
receptor activity because recent studies have shown that several
classes of general anesthetics modulate the function of this receptor.
GABAA receptor activity was assayed by measuring the
GABA-induced current in Xenopus oocytes expressed with
human GABAA receptor alpha-1,
beta-1 and gamma-2L subunits.
-Chloralose produced a concentration-dependent potentiation of the
GABA-induced current with an EC50 value of 49 µM and a
maximal effect of 239% of control. Membrane current was not affected
by
-chloralose in the absence of GABA.
-Chloralose (100 µM)
increased the affinity for GABA 5-fold and produced a small (17%)
increase in the efficacy of GABA. Measurement of the reversal
potentials for the
-chloralose response suggested that the effect is
mediated through increased Cl
conductance. Studies of
-chloralose interactions with other allosteric modulators determined
that
-chloralose binds to a site on the GABAA receptor
complex distinct from the benzodiazepine, neurosteroid and barbiturate
sites. Chloral hydrate, trichloroethanol and urethane also augmented
GABA-induced currents.
-Chloralose had no effect on the
hydroxytryptamine-induced currents in oocytes expressed with the
5-hydroxytryptamine3 receptor. These data extend the number
of classes of anesthetics that allosterically modulate GABAA receptor activity and indicate that GABAA
receptors may be a common site of action for diverse classes of general
anesthetics.
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