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Potent activation of dopamine D 3 /D 2 heterodimers by the antiparkinsonian agents, S32504, pramipexole and ropinirole
Author(s) -
Maggio Roberto,
Scarselli Marco,
Novi Francesca,
Millan Mark J.,
Corsini Giovanni U.
Publication year - 2003
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.2003.02038.x
Subject(s) - ropinirole , pramipexole , receptor , chemistry , dopamine receptor d3 , pharmacology , adenylyl cyclase , dopamine receptor d2 , agonist , biology , medicine , biochemistry , dopamine agonist , disease , parkinson's disease
Recombinant, human dopamine D 3 and D 2 receptors form functional heterodimers upon co‐expression in COS‐7 cells. Herein, actions of the antiparkinsonian agents, S32504, ropinirole and pramipexole, at D 3 /D 2L heterodimers were compared to their effects at the respective monomers and at split, chimeric D 3trunk /D 2tail and D 2trunk /D 3tail receptors: the trunk incorporated transmembrane domains (TDs) I–V and the tail TDs VI and VII. In binding assays with the antagonist [ 3 H]nemonapride, all agonists were potent ligands of D 3 receptors showing, respectively, 100‐, 18‐ and 56‐fold lower affinity at D 2L receptors, mimicking the selective D 3 receptor antagonist, S33084 (100‐fold). At D 3trunk /D 2tail receptors, except for ropinirole, all drugs showed lower affinities than at D 3 sites, whereas for D 2trunk /D 3tail receptors, affinities of all drugs were higher than at D 2L sites. The proportion of high affinity binding sites recognized by S32504, pramipexole and ropinirole in membranes derived from cells co‐expressing D 3 and D 2L sites was higher than in an equivalent mixture of membranes from cells expressing D 3 or D 2L sites, consistent with the promotion of heterodimer formation. In contrast, the percentage of high and low affinity sites (biphasic isotherms) recognized by S33084 was identical. Functional actions were determined by co‐transfection of a chimeric adenylyl cyclase (AC)‐V/VI insensitive to D 3 receptors. Accordingly, D 3 receptor‐transfected cells were irresponsive whereas, in D 2L receptor‐transfected cells, agonists suppressed forskolin‐stimulated cAMP production with modest potencies. In cells co‐transfected with D 3 and D 2L receptors, S32504, ropinirole and pramipexole potently suppressed AC‐V/VI with EC 50 s 33‐, 19‐ and 11‐fold lower than at D 2L receptors, respectively. S32504 also suppressed AC‐V/VI activity at split D 3trunk /D 2tail and D 2trunk /D 3tail chimeras transfected into COS‐7 cells. In conclusion, antiparkinson agents behave as potent agonists at D 3 /D 2 ‘heterodimers’, though any role in their actions in vivo remains to be demonstrated.