A novel a-conotoxin discriminates between rat a9a10 and a7 nicotinic receptors

MCINTOSH M; PLAZAS PV; WATKINS M; GOMEZ-CASATI M; MEYER, EL; OLIVERA BM; ELGOYHEN AB

Congreso; Society for Neuroscience 35th Annual Meeting; 2005

Society for Neuroscience

The a9 and a10 nicotinic acetylcholine receptor (nAChR) subunits are expressed in the cochlea as well as in dorsal root ganglion neurons, peripheral blood lymphocytes, developing thymocytes and skin.  In the inner ear, a9a10 co-assemble to form the receptor that mediates synaptic transmission between efferent olivochoclear fibers and hair cells of the cochlea, whereas, the function of a9 and a10 subunits in other tissues is less clear.  Additionally, non-cochlear expression of a9 and a10 generally occurs with expression of other nAChR subunits, including the closely related a7 subunit.  We now report the cloning and characterization of a novel toxin ƒna-conotoxin PeIA (a-CTx PeIA), that discriminates between a9a10 and a7 nAChRs.  The predicted mature toxin was synthesized and displayed a 260-higher selectivity for a-bungarotoxin-sensitive a9a10 nAChRs compared to a-bungarotoxin-sensitive a7 receptors.  The IC50 of the toxin was 6.9 ¡Ó 0.5 nM and 4.4 ¡Ó 0.5 nM, for recombinant and wild-type hair cells a9a10-containing nAChRs, respectively. The sequence of a-CTx PeIA bears high resemblance to a-conotoxins MII (a-CTx MII) and GIC (a-CTx GIC) isolated from Conus magus and Conus geographus, respectively. However, neither a-CTx MII nor a-CTx GIC at concentrations of 10 mM, blocked ACh responses elicited in Xenopus oocytes injected with the a9 and a10 subunits. Among neuronal non-a-bungarotoxin sensitive receptors, a-CTx PeIA was also active at a3b2 receptors. a-CTx PeIA represents a novel probe to differentiate responses mediated either through a9a10 or a7 nAChRs in those tissues where both receptors are expressed.