alpha-Bungarotoxin-sensitive nicotinic receptors on XXXX chromaffin cells: molecular cloning, functional expression and alternative splicing of the alpha 7 subunit.

@entity1238 @entity535 @entity1573 @entity969 @entity35 @entity291 @entity934
Chromaffin cells from the @entity291 adrenal medulla express alpha-bungarotoxin-sensitive @entity934 receptors whose subunit composition is unknown. Northern blot analysis showed that the alpha 7 subunit, a main component of these alpha-bungarotoxin-sensitive @entity934 receptors in avian and @entity35 brain, is expressed in chromaffin cells. The cDNA of this @entity291 alpha 7 subunit was cloned by polymerase chain reaction amplification of adrenal medulla RNA for detailed characterization of structure and function. The protein-coding region revealed 92% @entity535 sequence identity to @entity35 alpha 7 and 89% to @entity1573 alpha 7 subunits. The alpha-bungarotoxin affinity of alpha 7 homomers expressed in @entity1238 oocytes was similar to that observed previously with native chromaffin alpha-bungarotoxin-sensitive @entity934 receptors. Cross-linking and @entity969 gradient experiments suggested that, like the muscular and neuronal @entity934 receptors; the alpha 7 receptor has a pentameric structure. Upon activation with nicotinic agonists the alpha 7 receptor exhibited rapidly desensitizing cation currents that were blocked by nicotinic antagonists and showed inward rectification. The amplification of adrenal medulla RNA by reverse transcription-polymerase chain reaction methods revealed an alternatively spliced isoform of the @entity291 alpha 7 subunit, where the exon that codes for the M2 transmembrane segment was skipped during mRNA processing. Oocyte expression of this isoform does not yield functional channels. However, this alternative mRNA exhibits dose-dependent inhibition of alpha 7 homomer expression when coinjected with the undeleted isoform.
