FUNCTIONAL CONTRIBUTION OF THE ALPHA-5 SUBUNIT TO NEURONAL NICOTINIC CHANNELS EXPRESSED BY CHICK SYMPATHETIC-GANGLION NEURONS

1. Heterologous expression studies of the alpha 5 subunit of the neuro nal acetylcholine receptor (nAChR) gene family have demonstrated that it can participate in the function of ACh-gated channels if co-ex-pres sed with another alpha- and a beta-subunit. Previous studies also indi cate prominent expression of alpha 5 in both central and peripheral ne rvous systems. The participation of alpha 5 in native nAChRs and its f unctional role in these channels is, however, unknown. 2. In this stud y, we present evidence that alpha 5 has a role in at least two distinc t subtypes of nAChR complexes expressed by embryonic chick sympathetic neurones. 3. alpha 5 contributes not only to agonist but also to anta gonist sensitivity of natively expressed nAChR channels. Functional de letion of the alpha 5 subunit by antisense oligonucleotide treatment r emoves the nAChRs with relatively low affinity to ACh and cytisine. De letion of alpha 5 also eliminates channels that are blocked by the alp ha 7-specific antagonist methyllycaconitine (MLA) while increasing the percentage of current carried by nAChRs that are sensitive to alpha-b ungarotoxin (alpha-BgTx). 4. Single channel analyses indicate that fun ctional deletion of alpha 5 results in the deletion of both the 'brief ' and 'long' open duration, 50 pS subtypes of nAChR channels while inc reasing the expression of the 18 pS, alpha-BgTx-sensitive native nAChR s normally detected in sympathetic neurones at later developmental sta ges. 5. The biophysical and pharmacological profiles of native nAChRs revealed by this study and previous work are discussed in the context of a proposed model of the nAChR channels expressed by chick sympathet ic neurones throughout development.