Summary: Channel Opening by Anesthetics and GABA Induces Similar Changes in
the GABAA Receptor M2 Segment
Ayelet Rosen, Moez Bali, Jeffrey Horenstein, and Myles H. Akabas
Departments of Physiology and Biophysics and of Neuroscience, Albert Einstein College of Medicine, Yeshiva University, Bronx, New York
ABSTRACT For many general anesthetics, their molecular basis of action involves interactions with GABAA receptors.
Anesthetics produce concentration-dependent effects on GABAA receptors. Low concentrations potentiate submaximal GABA-
induced currents. Higher concentrations directly activate the receptors. Functional effects of anesthetics have been char-
acterized, but little is known about the conformational changes they induce. We probed anesthetic-induced conformational changes
in the M2 membrane-spanning, channel-lining segment using disulfide trapping between engineered cysteines. Previously, we
showed that oxidation by copper phenanthroline in the presence of GABA of the M2 69 cysteine mutants, a1T261Cb1T256C and
a1b1T256C resulted in formation of an intersubunit disulfide bond between the adjacent b-subunits that significantly increased the
channels' spontaneous open probability. Oxidation in GABA's absence had no effect. We examined the effect on a1T261Cb1T256C
and on a1b1T256C of oxidation by copper phenanthroline in the presence of potentiating and directly activating concentrations of
the general anesthetics propofol, pentobarbital, and isoflurane. Oxidation in the presence of potentiating concentration of anesthetics
had little effect. Oxidation in the presence of directly activating anesthetic concentrations significantly increased the channels'
spontaneous open probability. We infer that activation by anesthetics and GABA induces a similar conformational change at the M2
segment 69 position that is related to channel opening.
The GABAA receptors are a major molecular target for
general anesthetics such as pentobarbital, propofol, and