Journal of Neuroscience, Vol 9, 2423-2431, Copyright © 1989 by Society for Neuroscience
Characterization of nicotinic receptors in chick retina using a snake venom neurotoxin that blocks neuronal nicotinic receptor function
RH Loring, E Aizenman, SA Lipton and RE Zigmond
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts.
Nicotinic receptor function has been described in the retinas of a variety
of vertebrate species. Neuronal bungarotoxin (NBT, also known as
bungarotoxin 3.1, toxin F, or kappa-bungarotoxin) blocks nicotinic
receptors in several neuronal preparations, while the neuromuscular
antagonist alpha-bungarotoxin (BGT) fails to block most of these receptors.
NBT (100 nM), but not BGT (10 microM), substantially blocks nicotinic
function on ganglion cells in intact chick retina. 125I-NBT binds to 2
sites in homogenates of chick retina; one site that is shared with BGT (Kd
= 5-7 nM, Bmax approximately 500 fmol/retina) and one which is not (Kd =
2-3 nM, Bmax approximately 100 fmol/retina). 125I-NBT binding to the
NBT-specific site (binding in the presence of 1 microM unlabeled BGT) is
localized to 2 bands in the inner plexiform layer, corresponding to regions
richly innervated by neurons containing immunoreactivity for choline
acetyltransferase. Furthermore, this binding is blocked by competitive
nicotinic agonists and antagonists, but nicotine or other nicotinic
agonists do not displace 125I-NBT binding with very high affinity relative
to the displacement of 3H- nicotine reported by others in brain. Thus, of
the 2 NBT binding sites, the site not recognized by BGT most likely
represents functional nicotinic receptors in the chick retina, but these
receptors have relatively low affinity for nicotinic agonists, similar to
nicotinic receptors found in autonomic ganglia.