Modulation of the mammalian GABA_A receptor by type I and type II positive allosteric modulators of the α7 nicotinic acetylcholine receptor

Abstract

Background and Purpose: Positive allosteric modulators of the α7 nicotinic acetylcholine (nACh) receptor (α7-PAMs) possess promnesic and procognitive properties and have potential in the treatment of cognitive and psychiatric disorders including Alzheimer's disease and schizophrenia. Behavioural studies in rodents have indicated that α7-PAMs can also produce antinociceptive and anxiolytic effects that may be associated with positive modulation of the GABA A receptor. The overall goal of this study was to investigate the modulatory actions of selected α7-PAMs on the GABA A receptor.Experimental Approach: We employed a combination of cell fluorescence imaging, electrophysiology, functional competition and site-directed mutagenesis to investigate the functional and structural mechanisms of modulation of the GABA A receptor by three representative α7-PAMs.

Mutational Analysis of Anesthetic Binding Sites and Their Effects on GABAA Receptor Activation and Modulation by Positive Allosteric Modulators of the α7 Nicotinic Receptor

“…Our molecular docking and molecular dynamics studies indicate that the α7-PAMs NS-1738 and PAM-2 bind to the intersubunit interfaces in the transmembrane domain of the GABA A receptor. This is supported by previous functional data demonstrating a reduction or loss of potentiation by α7-PAMs of receptors activated by drugs binding to the anesthetic binding sites in the transmembrane domain [ 22 ]. In the present study, we have also shown that NS-1738 and PAM-2 protect against pCMB-induced chemical modification of the α1(L231C) residue at the β+/α− interface.…”

“…In rodents, administration of α7-PAMs such as PNU-120596 or PAM-2 improves the auditory gating deficit caused by amphetamine and recognition memory and cognitive flexibility in the MK-801 model of schizophrenia [ 44 , 45 , 46 ]. The present, as well as prior [ 22 ], data indicate that α7-PAMs can potentiate several common subtypes of the GABA A receptor through interactions with the classic anesthetic binding sites. However, given their relatively low efficacies, α7-PAMs are expected to competitively inhibit GABA A receptor potentiation by propofol or etomidate and any resulting behavior.…”

“…The conclusions of this study ultimately arise from the comparison of the magnitude of potentiation at a single concentration of a compound. The concentrations of the α7-PAMs, anesthetics, and 3α5βP used are saturating in the wild-type receptor [ 14 , 15 , 18 , 22 , 43 ], and thus reflect maximal potentiation and a true value of c compound . There is, however, no definite evidence that the same concentrations of the compounds are saturating in the mutant receptors.…”

“…In all experiments, NS-1738 and PAM-2 were tested at 50 µM, which is a near-saturating concentration in the α1β2γ2L receptor [ 22 ]. The parameter c α7-PAM that reflects gating efficacy (ratio of equilibrium dissociation constants in the active and resting receptors) was calculated as follows: …”

“…The sedative anesthetic etomidate, for example, binds to the β+/α− interface, whereas a barbiturate derivative binds with high affinity to the α+/β− and γ+/β− interfaces [ 20 , 21 ]. We recently showed that type I and type II positive allosteric modulators (PAMs) of the α7 nicotinic receptor N -(5-Cl-2-hydroxyphenyl)- N ′-[2-Cl-5-(trifluoromethyl)phenyl]-urea (NS-1738) and ( E )-3-(furan-2-yl)- N -( p -tolyl)-acrylamide (PAM-2) ( Figure 1 ) potentiate the α1β2γ2L GABA A receptor through interactions with anesthetic binding sites [ 22 ]. Here, we have employed mutational analysis to investigate in detail the involvement and contributions made by the individual intersubunit interfaces to receptor modulation by NS-1738 and PAM-2.…”