AGONIST PHARMACOLOGY OF THE NEURONAL ALPHA-7 NICOTINIC RECEPTOR EXPRESSED IN XENOPUS-OOCYTES

The potencies and efficacies of seven agonists at chick alpha7 nicotin ic receptors expressed in Xenopus oocytes were determined by whole cel l recording. (+)-Anatoxin-a was the most potent agonist (EC50 = 0.58 m uM) and acetylcholine was the least potent (EC50 = 320 muM). The rank order of agonist potencies was: (+)-anatoxin-a >> cytisine > (-)-nicot ine > (+)-nicotine > DMPP > 1-acetyl-4-methylpiperazine methiodide > a cetylcholine. DMPP evoked only very small currents: comparison of maxi mally effective agonist concentrations showed that DMPP was only one-f ifth as efficacious as other agonists. Previously published IC50 value s for rat brain I-125!alpha-bungarotoxin sites show a similar agonist profile, and the identity of homo-oligomeric alpha7 receptors with na tive alpha-bungarotoxin-sensitive neuronal nicotinic receptors is disc ussed.