Pseudophrynaminol: a potent noncompetitive blocker of nicotinic receptor-channels

(+/-)-Pseudophrynaminol inhibited carbamylcholine-elicited sodium-22 influx with an IC50 value of about 0.3 microM in both rat pheochromocytoma PC12 cells (ganglionic-type nicotinic receptor) and human medulloblastoma TE671 cells (neuromuscular-type nicotinic receptor). The inhibition in both cell lines appeared to be noncompetitive in nature. In rat cerebral cortical membranes, pseudophrynaminol had only low affinity (Ki 35 microM) for the agonist site on central nicotinic receptors at which [3H]nicotine binds. Pseudophrynaminol, at 10 microM, had marginal effects on a variety of other central receptors, and even at 100 microM inhibited batrachotoxin-elicited sodium-22 influx in a synaptoneurosomal preparation by only 40%. It had no effect at 30 microM on acetylcholinesterase and was a weak inhibitor of butyrylcholinesterase. Thus, pseudophrynaminol appears to be a potent, rather specific, noncompetitive inhibitor of ganglionic and neuromuscular nicotinic receptor-channels.