Functional Contribution of Neuronal AChR Subunits Revealed by Antisense Oligonucleotides

Abstract

Although multiple related genes encoding nicotinic acetylcholine receptor (AChR) subunits have been identified, how each of these subunits contributes to AChRs in neurons is not known. Sympathetic neurons express four classes of AChR channels and six AChR subunit genes (α3, α4, α5, α7, β2, and β4). The contribution of individual subunits to AChR channel subtypes in these neurons was examined by selective deletion with antisense oligonucleotides. An α3 antisense oligonucleotide decreased the number and altered the properties of the normally expressed AChactivated channels. The remaining AChR channels have distinct biophysical and pharmacological properties that indicate an important functional contribution of the α7 subunit.

The long internal loop of the α3 subunit targets nAChRs to subdomains within individual synapses on neurons in vivo

“…The nAChRs are concentrated in the postsynaptic membrane from the earliest stages of synapse formation, and these clusters are coextensive with the postsynaptic density at the synapse 22 . Levels of α3 regulate the degree of expression of functional nAChRs on both ciliary and sympathetic ganglion neurons in vivo and in vitro 23,24,25 . The α3 cytoplasmic loop targets to the synapse in vivo (this study).…”

Agonist pharmacology of the neuronal α7 nicotinic receptor expressed in Xenopus oocytes

“…Until the cloning and characterisation of the ~27 cDNA, the rela~onship between brain olBgt binding sites and nAChR was ambiguous [6]: although olBgt binding sites have a clear nicotinic profile in binding assays [7], the failure of clBgt to antagonise the majority of centrally-mediated nicotinic responses raised questions about the function of these proteins. More recent studies on autonomic neurons [8,9] have revealed that aBgt-sensitive nAChR are functional but their activity is eclipsed by the dominant nAChR subtype mediating conventional synaptic transmission. In the CNS, it is not known if aBgt-sensitive nAChR perform the same fictions as in autonomic Xetwpus oocytes were injected with 2 ng of a7 cDNA [l]" Electrophysiological recording was performed 2-5 days later using a conventional dual electrode voltage clamp.…”

Nicotinic Acetylcholine Receptors

“…The pattern of subunit expression, immunoprecipitation and antisense data all agree in recognising a major role to α3β4* type receptors in autonomic ganglion neurones, including chromaffin cells (Listerud et al, 1991;Rust et al, 1994;Conroy & Berg, 1995;Campos-Caro et al, 1997; but see Skok et al, 1999 andKlimaschewski et al, 1994). In chick ciliary ganglia these receptors contain also the α5 subunit: additionally a significant fraction of them contains both the α5 and the β2 subunit (reviewed in Berg et al, 2000).…”