Abstract
Two probes previously shown to distinguish the nicotinic ACh receptor of chick ciliary ganglion neurons also recognize a component on the surface of bovine chromaffin cells in culture that displays the properties expected for the chromaffin nicotinic ACh receptor. The first probe is a monoclonal antibody, mAb 35, raised against ACh receptor from Electrophorus electric organ, and the second is an alpha- neurotoxin, Bgt 3.1, purified from B. multicinctus venom. mAb 35 binds specifically to a single class of high-affinity sites on the chromaffin cells in culture. Scatchard analysis indicates a KD of 2.1 +/- 0.2 nM for the binding and a Bmax of 1.6 +/- 0.1 X 10(4) mAb 35 sites per cell. The number of sites on the cells can be reduced through modulation by exposure of the cells to Bgt 3.1. The modulation can be blocked by the cholinergic ligands d-tubocurarine and carbamylcholine. Long-term exposure to the agonist carbamylcholine alone also reduces the number of mAb 35 binding sites. Bgt 3.1 inhibits nicotine-induced catecholamine release from the cells to the same extent and with the same concentration dependence that it modulates the number of mAb 35 sites on the cells. In addition, mAb 35 treatment of the cells causes a specific and almost complete blockade of nicotine-induced catecholamine release, apparently through a modulation of the receptor. These results indicate that the bovine chromaffin component recognized by mAb 35 and Bgt 3.1 is likely to be the nicotinic ACh receptor on the cells and that it has many similarities to ACh receptors on chick autonomic neurons.