Cholinergic receptors on cultured neurones from the central nervous system of embryonic cockroaches.

Cultured neurones from the cockroach, Periplaneta americana, have been used to investigate putative acetylcholine receptors. Ligand-binding experiments revealed that these neurones possessed an alpha-bungarotoxin binding site that was saturable, had an apparent affinity constant of 3.51 nM and was predominantly nicotinic in nature. An individual culture of 50,000 neurones had a maximum of 4200 pmol. binding sites per gram of protein. [I125]alpha-BTX autoradiography showed the binding sites to be distributed over both the neuronal cell bodies and their associated axonal processes. Both acetylcholine and nicotine applied by pressure ejection to the neuronal soma induced depolarizing responses and in the majority of cells tested the response was blocked by alpha-BTX at a concentration of 25 nM in a time dependent manner. Some of the neurones, however, were depolarized by acetylcholine and nicotine after 3 h incubation in alpha-BTX. These experiments suggest that two populations of cells possessing extrajunctional nicotinic receptors were present in these cultures. In the majority of cells these receptors were sensitive to alpha-BTX but in a subpopulation the receptors were unaffected by this toxin.