Channel properties of an insect neuronal acetylcholine receptor protein reconstituted in planar lipid bilayers

Abstract

A pentameric membrane protein composed of four types of polypeptide has been identified as the minimal structural unit responsible for the electrogenic action of acetylcholine on electrocytes and muscle cells^1–3. Because many populations of central and peripheral neurones also have nicotinic acetylcholine receptors (AChRs), considerable effort has recently gone into identifying the neuronal receptor^4,5. The central nervous tissue of insects contains very high concentrations of nicotinic AChRs^6,7, and we have recently purified an α-toxin binding protein, a putative AChR, from neuronal membranes of locusts^8,9. It is a component of high relative molecular mass, clearly composed of identical subunits, a structure predicted for an ancestral AChR protein^10,11. To verify that the purified polypeptides not only represent ligand binding sites but that they are indeed functional receptors, we have now reconstituted the isolated protein in a planar lipid bilayer. We show that in this system cholinergic agonists activate functional ion channels, that have properties comparable to those exhibited by the peripheral AChRs in vertebrates; thus, for the first time a functional acetylcholine receptor channel has been indentified in nerve cells.