A Novel alpha -Conotoxin, PeIA, Cloned from Conus pergrandis, Discriminates between Rat alpha 9 alpha 10 and alpha 7 Nicotinic Cholinergic Receptors

The alpha 9 and alpha 10 nicotinic cholinergic subunits assemble to form the receptor believed to mediate synaptic transmission between efferent olivocochlear fibers and hair cells of the cochlea, one of the few examples of postsynaptic function for a non-muscle nicotinic acetylcholine receptor (nAChR). However, it has been suggested that the expression profile of alpha 9 and alpha 10 overlaps with that of alpha 7 in the cochlea and in sites such as dorsal root ganglion neurons, peripheral blood lymphocytes, developing thymocytes, and skin. We now report the cloning, total synthesis, and characterization of a novel toxin alpha -conotoxin PeIA that discriminates between alpha 9 alpha 10 and alpha 7 nAChRs. This is the first toxin to be identified from Conus pergrandis, a species found in deep waters of the Western Pacific. alpha -Conotoxin PeIA displayed a 260-fold higher selectivity for alpha -bungarotoxin-sensitive alpha 9 alpha 10 nAChRs compared with alpha -bungarotoxin-sensitive alpha 7 receptors. The IC sub(50) of the toxin was 6.9 plus or minus 0.5 nM and 4.4 plus or minus 0.5 nM for recombinant alpha 9 alpha 10 and wild-type hair cell nAChRs, respectively. alpha -Conotoxin PeIA bears high resemblance to alpha -conotoxins MII and GIC isolated from Conus magus and Conus geographus, respectively. However, neither alpha -conotoxin MII nor alpha -conotoxin GIC at concentrations of 10 mu M blocked acetylcholine responses elicited in Xenopus oocytes injected with the alpha 9 and alpha 10 subunits. Among neuronal non- alpha -bungarotoxin-sensitive receptors, alpha -conotoxin PeIA was also active at alpha 3 beta 2 receptors and chimeric alpha 6/ alpha 3 beta 2 beta 3 receptors. alpha -Conotoxin PeIA represents a novel probe to differentiate responses mediated either through alpha 9 alpha 10 or alpha 7 nAChRs in those tissues where both receptors are expressed.