Desformylflustrabromine Modulates a4b2 Neuronal Nicotinic Acetylcholine Receptor High- and Low-Sensitivity Isoforms at Allosteric Clefts Containing the b2 Subunit

Alterations in expression patterns of a4b2 nicotinic acetylcholine receptors have been demonstrated to alter cholinergic neurotransmission and are implicated in neurologic disorders, including autism, nicotine addiction, Alzheimer’s disease, and Parkinson’s disease. Positive allosteric modulators (PAMs) represent promising new leads in the development of therapeutic agents for the treatment of these disorders. This study investigates the involvement of the b2-containing subunit interfaces of a4b2 receptors in the modulation of acetylcholine (ACh)-induced responses by the PAM desformylflustrabromine (dFBr). Eight amino acids on the principal face of the b2 subunit were mutated to alanine to explore the involvement of this region in the potentiation of ACh-induced currents by dFBr. AChinduced responses obtained from wild-type and mutant a4b2 receptors expressed in Xenopus laevis oocytes were recorded in the presence and absence of dFBr using two-electrode voltage clamp electrophysiology. Wild-type and mutant receptors were expressed in both high and low ACh sensitivity isoforms by using biased injection ratios of 1:5 or 5:1 a4 to b2 complementary RNA. Mutations were made in the B, C, and A loops of the principal face of the b2 subunit, which are regions not involved in the binding of ACh. Mutant b2(Y120A) significantly eliminated dFBr potency in both isoform preparations. Several other mutations altered dFBr potentiation levels in both preparations. Our findings support the involvement of the principal face of the b2 subunit in dFBr modulation of ACh-induced responses. Findings from this study will aid in the improved design of dFBrlike PAMs for potential therapeutic use.