The alpha7 nicotinic acetylcholine receptor subunit exists in two isoforms that contribute to functional ligand-gated ion channels.
Fast synaptic transmission in mammalian autonomic ganglia is mediated primarily by nicotinic receptors, and one of the most abundant nicotinic acetylcholine receptor subtypes in these neurons contains the alpha7 subunit (alpha7-nAChRs). Unlike alpha7-nAChRs expressed in other cells, the predominant alpha7-nAChR subtype found in rat intracardiac and superior cervical ganglion neurons exhibits a slow rate of desensitization and is reversibly blocked by alpha-bungarotoxin (alphaBgt). We report here the identification of an alpha7 subunit sequence variant in rat autonomic neurons that incorporates a novel 87-base pair cassette exon in the N terminus of the receptor and preserves the reading frame of the transcript. This alpha7 isoform was detected using reverse transcriptase-polymerase chain reaction techniques in neonatal rat brain and intracardiac and superior cervical ganglion neurons. Immunoblot experiments using a polyclonal antibody directed against the deduced amino acid sequence of the alpha7-2 insert showed a pattern of expression consistent with alpha7-2 subunit mRNA distribution. Moreover, the alpha7-2 subunit could be immunodepleted from protein extracts by solid-phase immunoprecipitation techniques using the anti-alpha7 monoclonal antibody 319. The alpha7-2 subunit was shown to form functional homomeric ion channels that were activated by acetylcholine and blocked by alpha-bungarotoxin when expressed in Xenopus laevis oocytes. This alpha7 isoform exhibited a slow rate of desensitization, and inhibition of these channels by alphaBgt reversed rapidly after washout. Taken together, these data indicate that the alpha7-2 subunit is capable of forming functional alphaBgt-sensitive acetylcholine receptors that resemble the alpha7-nAChRs previously identified in rat autonomic neurons. Furthermore, the distribution of the alpha7-2 isoform is not limited to peripheral neurons.
Department of Pharmacology and Therapeutics, University of South Florida College of Medicine, 12901 Bruce B. Downs Boulevard, MDC 9, Tampa, FL 33612-4799, USA.
Emily G
EG
Severance
Hongling
H
Zhang
Yolmari
Y
Cruz
Sergei
S
Pakhlevaniants
Stephen H
SH
Hadley
Jahanshah
J
Amin
Lynn
L
Wecker
Crystal
C
Reed
Javier
J
Cuevas
D000109:Acetylcholine / Q000378:metabolism; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D007473:Ion Channels / Q000378:metabolism*; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D014982:Xenopus laevis; D064569:alpha7 Nicotinic Acetylcholine Receptor
C579165:Chrna7 protein, rat; D007473:Ion Channels; D020033:Protein Isoforms; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D000109:Acetylcholine