Abstract
Levels of acetylcholine (ACh) sensitivity and numbers of alpha- bungarotoxin (alpha-Bgt)-binding sites have been measured for chick ciliary ganglion neurons grown in cell culture under various conditions. The two properties were found not to change in parallel. Neurons maintained in culture medium supplemented with embryonic eye extract developed high levels of ACh sensitivity and low numbers of alpha-Bgt-binding sites, whereas neurons grown in medium containing elevated K+ concentrations displayed the reverse. Neurons from media containing both eye extract and elevated K+ concentrations had both low levels of sensitivity and low numbers of toxin sites. The growth conditions do not alter the basic binding properties of the ACh receptors and alpha-Bgt-binding sites. Both the ACh receptor dose- response characteristics and the pharmacological properties of the toxin-binding sites were similar for neurons grown in media containing eye extract or elevated K+ concentrations. The inhibitory effects of eye extract on development of alpha-Bgt-binding sites appeared to be specific: eye extract had previously been shown to stimulate neuronal growth and cholinergic development, and in the present study eye extract enhanced development of ACh sensitivity and had no effect on mechanisms responsible for binding and accumulation of tetanus toxin. Eye extract did not block alpha-Bgt binding in competition binding experiments and did not cause redistribution of toxin sites away from the neuronal soma. These results demonstrate that ACh sensitivity and alpha-Bgt-binding sites can be independently regulated on the neurons and suggest that the two membrane properties are associated with separate membrane components.