D4 DOPAMINE RECEPTOR-MEDIATED SIGNALING EVENTS DETERMINED IN TRANSFECTED CHINESE-HAMSTER OVARY CELLS

A Chinese hamster ovary (CHO) cell line stably expressing a recombinan t human D4 dopamine receptor made from a synthetic gene has been used to determine potential D4-mediated signaling events. We designed and s ynthesized a modified gene coding for a human D4 receptor with reduced G + C content but unaltered encoded amino acids. Stable expression of this gene was obtained in two cell lines, inducible expression in CHO locI cells and constitutive expression in HEK293 cells. In CHO lacI c ells induced to express D4 receptors but not in uninduced cells, dopam ine and quinpirole inhibit forskolin-stimulated cAMP accumulation and potentiate ATP-stimulated [H-3]arachidonic acid release through a mech anism that requires protein kinase C but is unaffected by membrane-sol uble cAMP analogs. In addition, D4 receptor activation causes an incre ase in the rate of extracellular acidification measured by microphysio metry. This response is unaffected by protein kinase C down-regulation but is inhibited by removal of extracellular sodium and inhibitors of NaH-1 exchange, suggesting the involvement of a Na+/H+ exchanger. All responses are blocked by clozapine and are sensitive to pertussis tox in. D4 receptors, like other G(i)/G(o)-linked receptors, mediate multi ple signaling events, and the pathways activated are similar to those used by D2 and D3 receptors expressed in similar cells.