Pharmacological and functional characterization of D2, D3 and D4 dopamine receptors in fibroblast and dopaminergic cell lines.

In order to study the properties of the D2-like dopamine receptors, D2, D3 and D4 clones were transfected into mouse Ltk- fibroblasts, CCL1.3, and a neuronal mesencephalic cell line, MN9D. Most of the derived antagonist and agonist inhibition constants were the same for a given receptor in either cell line as determined by saturation and competition binding experiments. The rank order potencies for antagonists are: eticlopride, D2 > D3 > D4; YM-09151-2, D2 = D4 > D3; spiperone, D2 = D3 > D4; (+)-butaclamol, D2 > D3 > D4; clozapine, D4 > D2 > D3; and for agonists, quinpirole, D3 = D4 > D2; 7-hydroxy-2-(di-n-propyl)-aminotetralin, D3 > D2 = D4. Functionally, D2 stimulation increases inositol phosphate levels in CCL1.3 cells but not in MN9D, whereas D2 activation inhibits forskolin-stimulated cyclic AMP levels in both cell lines. D4 stimulation has no effect on inositol phosphate metabolism in either cell type, but inhibits adenylate cyclase in MN9D cells. Both the D2 and D4 mediated decreases in cyclic AMP can be blocked by preincubation with pertussis toxin. D3 does not couple to these pathways in either cell line. Reverse transcription/polymerase chain reaction techniques were used to determine the availability of cellular signalling systems. Both CCL1.3 and MN9D cells have high levels of G alpha i2 expression, whereas neither cell expresses G alpha i1 or G alpha i3. These data imply that the D2 receptor couples to the G alpha i2 subtype in both cell lines, whereas D4 does not.(ABSTRACT TRUNCATED AT 250 WORDS)