Journal of Neuroscience, Vol 6, 3405-3412, Copyright © 1986 by Society for Neuroscience
Identification of a nicotinic acetylcholine receptor on neurons using an alpha-neurotoxin that blocks receptor function
SW Halvorsen and DK Berg
An alpha-neurotoxin, Bgt 3.1, that reversibly blocks the ACh response of
chick ciliary ganglion neurons has been used to identify 2 classes of
high-affinity binding sites on the cells in culture. The first class
appears to be the alpha-bungarotoxin binding site on the neurons. The
second class of Bgt 3.1 sites is distinct from the alpha-bungarotoxin
binding sites and has the properties expected for the functional nicotinic
ACh receptor on the cells. Equilibrium binding and kinetic studies indicate
a Kd value of 5-6 nM for Bgt 3.1 at the second class of sites. The kinetics
and affinity of binding are consistent with those inferred from previous
physiological studies for Bgt 3.1 inhibition of receptor function. Bgt 3.1
binding to the sites is completely inhibited by each of the cholinergic
ligands ACh, carbachol, nicotine, d-tubocurarine, and trimethaphan, but not
by alpha- bungarotoxin. Highest site densities are found in cultures of
ciliary and sympathetic ganglion neurons, cell types known to have
ganglionic nicotinic ACh receptors. Low levels of sites may be present in
cultures of spinal cord and dorsal root ganglion neurons; no binding is
found in cultures of skeletal myotubes or cardiac cells when
alpha-bungarotoxin is used to block Bgt 3.1 binding to alpha-bungarotoxin
sites. These results demonstrate that Bgt 3.1 can be used as a specific
probe for the nicotinic ACh receptor on chick autonomic neurons.