Eur J Pharmacol 1994 Nov 15;2693:375-9. doi: 10.1016/0922-4106(94)90045-0.

Block by apomorphine of acetylcholine receptor channels expressed in Xenopus oocytes.

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Effects of apomorphine and other compounds related to dopamine receptors on nicotinic acetylcholine receptor channels were investigated by expressing functional channels in Xenopus oocytes. When channels were expressed with a combination of alpha 3 and beta 4 subunits, acetylcholine activated an inward current, and apomorphine suppressed the current in a concentration-dependent manner with an IC50 value of about 3 microM. SKF38393 (R(+)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol; dopamine D1 receptor agonist; 3 and 30 microM), quinpirole (dopamine D2 receptor agonist; 30 microM), SCH23390 (R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benza zepine; dopamine D1 receptor antagonist; 10 microM) or sulpiride (dopamine D2 receptor antagonist; 10 microM) also inhibited the acetylcholine-activated current whereas dopamine (100 microM) was ineffective. The inhibition by apomorphine of the acetylcholine-activated current was also apparent when alpha 3 subunit was combined with beta 2 subunit instead of beta 4 subunit, or beta 4 subunit was combined with alpha 2 or alpha 4 subunit instead of alpha 3 subunit to express channels. The results suggest that apomorphine blocks acetylcholine receptor channels through a binding site that is similar to, but cannot be included in dopamine receptors. The binding site may not be present in a single specific subunit.

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