Presence of multiple binding sites on α9α10 nAChR receptors alludes to stoichiometric-dependent action of the α-conotoxin, Vc1.1

Abstract

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels involved in fast synaptic transmission. nAChRs are pentameric receptors formed from a combination of different or similar subunits to produce heteromeric or homomeric channels. The heteromeric, α9α10 nAChR subtype is well-known for its role in the auditory system, being expressed in cochlear hair cells. These nAChRs have also been shown to be involved in immune-modulation. Antagonists of α9α10 nAChRs, like the α-conotoxin Vc1.1, have analgesic effects in neuropathic pain. Unlike other nAChR subtypes there is no evidence that functional receptor stoichiometries of α9α10 exist. By using 2-electrode voltage clamp methods and maintaining a constant intracellular Ca2+ concentration, we observed a biphasic activation curve for ACh that is dependent on receptor stoichiometry. Vc1.1, but not the α9α10 antagonists RgIA or atropine, inhibits ACh-evoked currents in a biphasic manner. Characteristics of the ACh and Vc1.1 activation and inhibition curves can be altered by varying the ratio of α9 and α10 mRNA injected into oocytes, changing the curves from biphasic to monophasic when an excess of α10 mRNA is used. These results highlight the difference in the pharmacological profiles of at least two different α9α10 nAChR stoichiometries, possibly (α9)3(α10)2 and (α9)2(α10)3. As a result, we infer that there is an additional binding site for ACh and Vc1.1 at the α9-α9 interface on the hypothesized (α9)3(α10)2 nAChR, in addition to the α10-α9 and or α9-α10 interfaces that are common to both stoichiometries. This study provides further evidence that receptor stoichiometry contributes another layer of complexity in understanding Cys-loop receptors.

Pharmacological characterization of conotoxin lt14a as a potent non-addictive analgesic

“…nAChR subtypes and Nmethyl-D-aspartate (NMDA) receptors are the two main receptors utilized by conotoxins that were reported to have analgesic properties (Lewis et al, 2012). By targeting a9a10-nAChRs, a-conotoxin Vc1.1, RgIA and PeIA plays a role in immune responses and pain (Indurthi et al, 2014a;Lewis et al, 2012;McIntosh et al, 2009;Satkunanathan et al, 2005). Conotoxin lt14a contains 13 amino acids with a disulfide bridge pattern that is assumed to be connected as Cys1-Cys3, Cys2-Cys4.…”

“…The traditional antinociceptive opioid drugs, such as morphine and pethidine, show a powerful antinociceptive efficacy; however, the development of tolerance and physical dependence is also a universal characteristic of these drugs (Chindo et al, 2009). As promising antinociceptive drugs, MVIIA, CVID, Vc1.2, m-and mO-conotoxins show efficient antinociceptive properties by targeting different molecular receptors (Indurthi et al, 2014b;Jayamanne et al, 2013;Klotz, 2006;Knapp et al, 2012;Wallace et al, 2008).…”

Conotoxins Targeting Nicotinic Acetylcholine Receptors: An Overview

“…Recently, Indurthi et al (2014) [32] proposed that a fourth possible binding site might exist, i.e. , α 9 α 9.…”

αS-conotoxin GVIIIB potently and selectively blocks α9α10 nicotinic acetylcholine receptors

“…For this reason, it was previously assumed that the α9 subunit was analogous to other nAChR α subunits in providing the principal binding site, whereas the α10 subunit functions similar to neuronal nAChR β subunits in providing a complementary binding site. However, α-conotoxins that bind to the α9α10 nAChR appear to bind to an interface formed by the α10/α9 subunit interface rather than the α9/α10 interface (37) (42) (43). We therefore sought to examine whether block of the α9α10 nAChR by αS-GVIIIB occurs at the same or different binding site than the α-conotoxins.…”