PHARMACOLOGICAL CHARACTERIZATION OF RECOMBINANT HUMAN NEURONAL NICOTINIC ACETYLCHOLINE-RECEPTORS H-ALPHA-2-BETA-2, H-ALPHA-2-BETA-4, H-ALPHA-3-BETA-2, H-ALPHA-3-BETA-4, H-ALPHA-4-BETA-2, H-ALPHA-4-BETA-4 AND H-ALPHA-7 EXPRESSED IN XENOPUS OOCYTES

Human neuronal nicotinic acetylcholine receptors (nAChRs) h alpha 2 be ta 2, h alpha 2 beta 4, h alpha 3 beta 2, h alpha 3 beta 4, h alpha 4 beta 2, h alpha 4 beta 4 and h alpha 7 were expressed in Xenopus oocyt es and tested for their sensitivities to the nicotinic agonists acetyl choline (ACh), nicotine, cytisine (CYT) and 1,1-dimethyl-4-phenylpiper azinium (DMPP) and the nAChR, antagonists mecamylamine (MEC), d-tubocu rarine and dihydro-beta-erythroidine. CYT was the least efficacious ag onist at hnAChRs containing beta 2 subunits, but it displayed signific ant activity at h alpha 2 beta 4, h alpha 3 beta 4, h alpha 4 beta 4 a nd h alpha 7 nAChRs. ACh was one of the most efficacious agonists at a li hnAChRs, except at h alpha 3 beta 2, where DMPP was markedly more e fficacious than ACh. ACh was among the least potent agonists at all hn AChRs. The rank order of potency displayed by h alpha 3 beta 2 and h a lpha 3 beta 4 nAChRs (DMPP approximate to CYT approximate to nicotine> ACh and DMPP > CYT approximate to nicotine>ACh, respectively), differs from that reported for their rat homologs (Luetje and Patrick, 1991; Covernton et al., 1994). The agonist profile observed in h alpha 7 als o differs from that reported for its rat homolog (Seguela et al., 1993 ). Human alpha 4 beta 2 and h alpha 4 beta 4 nAChRs were more sensitiv e to dihydro-beta-erythroidine than d-tubocurarine, whereas h alpha 7 and h alpha 3 beta 4 were more sensitive to d-tubocurarine than dihydr o-p-erythroidine. These antagonists were equipotent at h alpha 2 beta 2, h alpha 3 beta 2 and h alpha 2 beta 4 nAChRs. MEC (3 mu M) inhibite d h alpha 2 beta 4 and h alpha 4 beta 4 nAChRs by > 80%, whereas h alp ha 2 beta 2, h alpha 4 beta 2 and h alpha 7 nAChRs were inhibited by a pproximately 50%. Taken together, the differential sensitivities obser ved at various recombinant hnAChR subtypes indicate that both alpha an d beta subunits contribute to the pharmacology of these ligand-gated c hannels. The unique selectivity profiles displayed by human nAChRs con stitute a valuable tool for the development of selective nicotinic ana logs as potential therapeutic drugs.