Dopamine D1 receptor-mediated toxicity in human SK-N-MC neuroblastoma cells

Striatal degeneration occurs through unknown mechanisms in certain neurodegenerative disorders characterized by increased and sustained synaptic levels of dopamine. In the present studies, we examined the effects of treatment of SK-N-MC neuroblastoma cells with dopamine to understand the participation of dopamine D1 receptor in postsynaptic cytotoxicity. Treatment of SK-N-MC cells either with dopamine or the D1 receptor agonist SKF R-38393 resulted in a significant increase in the production of reactive oxygen species (by ∼2.75-fold) and cell death (∼50%), while antagonism of the D1 receptor with SCH 23390 significantly reversed (to ∼75% of control level) these effects. Accumulation of cAMP in dopamine treated cells (t1/2 = 1.5 h) preceded changes in ionic gradient (t1/2 = 6.5 h), as measured by intracellular potassium concentration and leakage of cytochrome c into the cytosol (t1/2 = 13 h), suggesting a possible staging of toxic events as a result of activation of D1 receptor by dopamine. Examination of cellular metabolic properties with 13C NMR spectroscopy showed an inhibitory effect on tricarboxylic acid cycle metabolism via D1-mediated receptors after treatment with dopamine, suggesting a direct role for D1 receptor in dopamine-induced postsynaptic cell death. The present studies provide novel insight into a possible patho-physiological staging of cytotoxic events that are mediated by activation of D1 receptor.