THE NEURONAL ALPHA(6) SUBUNIT FORMS FUNCTIONAL HETEROMERIC ACETYLCHOLINE-RECEPTORS IN HUMAN TRANSFECTED CELLS

We examine some of the biological and physiological properties of the avian alpha(6) neuronal nicotinic acetylcholine receptor (nAChR) subun it, We show here that, beginning at embryonic day 5, alpha(6) mRNA is abundantly expressed in the developing chick neuroretina, where it coe xists with other nicotinic receptor subunit mRNAs such as alpha(3), be ta(2) and beta(4). In contrast, alpha(6) mRNA is absent from the optic tectum and from the peripheral ganglia, Despite numerous efforts, the alpha(6) subunit has long failed the critical test of functional reco nstitution, Here we use patch-clamp techniques and confocal laser micr oscopy to measure ACh-activated currents and nicotine-elicited Ca2+ tr ansients in human BOSC 23 cells transfected with chick alpha(6) in com bination with other chick nAChR neuronal subunits. Heterologously expr essed alpha(6) and beta(4) subunits form functional heteromeric nAChRs , which are permeable to Ca2+ ions and blocked by the nicotinic antago nist methyllycaconitine (10 mu M). Likewise, ACh elicits measurable cu rrents in cells transfected with alpha(6) and beta(2). Hill analysis o f the dose-response curves in cells transfected with alpha(3), beta(4) and alpha(6) cDNAs, suggests the assembly of functional alpha(3) beta (4) alpha(6) receptor, with an apparent affinity for ACh threefold low er than alpha(3) beta(4). Our results indicate that alpha(6)-containin g nAChRs assemble in heterologous expression systems and are probably present in retinal cells.