Cyclothiazide selectively inhibits mGluR1 receptors interacting with a common allosteric site for non-competitive antagonists

Abstract

Metabotropic glutamate receptors mGluR1 and mGluR5 stimulate phospholipase C, leading to an increased inositol triphosphate level and to Ca 2+ release from intracellular stores. Cyclothiazide (CTZ), known as a blocker of AMPA receptor desensitization, produced a non-competitive inhibition of [Ca 2+ ] i increases induced by mGluR agonists in HEK 293 cells transfected with rat mGluR1a but had no effect on the [Ca 2+ ] i signals in cells expressing rat mGluR5a. In cells expressing mGluR1, CTZ also inhibited phoshoinositide hydrolysis, as well as cAMP accumulation and arachidonic acid release induced by mGluR1 agonists, indicating a direct inhibition of the receptor and not of a particular signal transduction system. However, CTZ failed to antagonize cAMP inhibition stimulated by rat mGluR2, -3, -4, -6, -7 and -8 receptors confirming its selectivity for mGluR1. The use of chimeric receptors with substituted N-terminal domains showed that CTZ did not interact with the N-terminal mGluR1a domain. Instead, mutation analysis revealed that CTZ interacts with the Thr-815 and Ala-818 residues, located at the 7 th transmembrane domain, similarly as the mGluR1-selective antagonist CPCCOEt. In primary cultures of cerebellar granule neurons, expressing native metabotropic and ionotropic glutamate receptors, the final outcome of CTZ effects depended on its combined ability to potentiate AMPA receptors and inhibit mGluR1a receptors.

Neuroprotective effect of Buyang Huanwu Decoction against focal cerebral ischemia/reperfusion injury in rats – Time window and mechanism

“…This may be a part of the neuroprotective mechanisms of BYHWD. Even though the specific mechanism of how BYHWD inhibits the release of glutamate and suppresses the expression of mGluR-1 RNA is unclear, it may be involved in calcium influx and calcium release (Mironov, 2008), release of arachidonic acid (Surin et al, 2007), and synthesis of nitric oxide (Chong et al, 2005). Therefore, a further study is needed.…”

Structure of a Class C GPCR Metabotropic Glutamate Receptor 1 Bound to an Allosteric Modulator

“…S12) (9). Examination of the contact residues in the binding pocket reveals only four residues of mGlu 1 that differ from mGlu 5 : V664 3.32 , S668 3.36 , T815 7.38 , and A818 7.41 , all of which have previously been implicated in subtype selectivity by mutagenesis-based studies (24–26). Therefore, we mutated these four residues to their corresponding amino acid in mGlu 5 (Fig.…”

Molecular Insights into Metabotropic Glutamate Receptor Allosteric Modulation

“…Substitution of mGlu 1 nonconserved amino acids onto the equivalent positions in mGlu 5 , and vice versa, resulted in gain-of-function of selective allosteric modulators (Litschig et al, 1999;Pagano et al, 2000;Knoflach et al, 2001;Goudet et al, 2005;Surin et al, 2007). These mutagenesis studies pointed to a common location for allosteric binding pockets for group I mGlu receptors.…”